Major Minor Dominant 7th Major 7th Minor 7th Suspended
When you form a bar chord, you will hold down all six strings (sometimes five) with a finger (usually the first finger, but not always). You will, in effect, use your finger as a "bar." These chords have a great advantage, for they can be moved anywhere on the neck to form just about any chord desired. The disadvantage is they are very hard to play. To play them well, and to be able to switch from one chord to another within a progression, is even harder. If you can't yet play bar chords, here are some exercises to help.

Figure 1 shows five bar chord forms for major chords: G, C, A (two forms), and E. These forms get their names from the chords used to derive them. For the E form, create an E chord, then move it one fret towards the guitar body to get an F (major) chord. Move it one more to get a Gb, and one more to get a G, and so on.

Since I cannot come close to playing the G form, I'll ignore it from this point forward. The first A form is also quite difficult (at least, I can't play it) -- you need to cram your second, third, and fourth fingers onto the the third fret of strings four, three, and two -- all while holding down five strings with your first finger. To do the second A form, you have to hold down three strings with your fourth finger, without touching the first string -- I can't play this either. The E form is easier (although it can still take months or more to learn to do it) -- I can play it, with difficulty. To get Gb, then G, then Ab, etc. -- just move the form, one fret at a time, toward the guitar body. If you examine the E form, and don't use the fifth or sixth strings (so you hold down only strings one and two with the first finger), you see that that is the usual form most players first learn when they learn F. And it's usually very difficult to learn even that form. It certainly was for me -- it took me months to master the four-string form of F.

The C form is a bit easier than the E form (at least for me, with my very long fingers). Most players first learn Db and Eb as shown, but without the fifth string. (The Eb form is derived by moving the Db form two frets toward the guitar body.) The form shown in Figure 1 is more desirable, since the first note of the chord (Db) is the bass note. Most players learn Bb as shown, in the first A form, but without the fifth string (so they need hold down only the first string with the first finger). Either A form shown in the Figure is better, again since the first note of the chord (Bb) is the bass note.
Figure 1. Bar Chord Forms For Major Chords.
For minor chords, there are two bar chord forms: Am and Em. See Figure 2. The Am form is similar to the A form for major chords. But it's a lot easier (at least for me). Most players first learn Bbm as shown, but without the fifth string (so they need hold down only the first string with the first finger). Then you can get Bm and Cm, and so on -- just by moving the form one fret at a time toward the guitar body.

Most players first usually learn Fm as shown, but without the fifth and sixth strings (so it's similar to the beginner's form for F major). In that case, you need only hold down strings one, two, and three with the first finger, then hold down the fourth string with the third finger. For beginners, this (easier) form is usually still quite difficult. Either way, you get Gbm, Gm, and Abm, and so on -- by moving the form one fret at a time toward the guitar body.

Figure 2. Bar Chord Forms For Minor Chords.
For (dominant) 7th chords, there are two bar chord forms: A7 and E7. See Figure 3. Most players first learn F7 as shown, but with an open fifth string, the first finger holding down the first four strings, and the third finger holding down the third string, second fret. That form is usually still quite difficult. The more difficult form shown has the advantage that the first note of the chord is the bass note. With either the E7 form shown, or the easier one, you then get Gb7, G7, Gb7, A7, and so on moving the form one fret at a time.

The A7 form shown is different from the usual A7 that beginners learn, but it has the advantage that, as it is moved along the neck, the first note of the chord is always the bass note.

Figure 3. Bar Chord Forms For (Dominant) Seventh Chords
For Major 7th chords, there are four bar chord forms: AMaj7, CMaj7, Dmaj7, and EMaj7. See Figure 4. The EMaj7 form is a lot like the E form (for Major chords, in Figure 1) and the Em form (for minor chords, in Figure 2). It is also probably the hardest (or second hardest) form. The DMaj7 form may be the most difficult; it is similar to the A form in Figure 1, and requires the player to hold down three strings with the fourth finger.

The CMaj7 form is very close to the C form in Figure 1, and relatively easy to play (if you have long fingers). As before, get more chords just by moving the positions along the neck.

Figure 4. Bar Chord Forms For Major Seventh Chords
For minor 7th chords, there are two forms: Am7 and Em7. See Figure 5. The Am7 form is quite similar to the AMaj7 form in Figure 4. The Em7 form is very similar to the E form in See Figure 1, and is a bit easier, since fewer strings need to be held down.

Figure 5. Bar Chord Forms For Minor Seventh Chords
The last bar chord forms I will show are those for suspended (same as suspended fourth) chords. There are two: Asus and Esus (also called the Asus4 and Esus4). See Figure 6. Recall that suspended fourth and suspended second chords are not independent (see this, for example). The Esus form has a lot in common with the E form in Figure 1, the Em form in Figure 2, and the E7 form in Figure 3. The Asus form is more difficult, since it requires more of a reach.

Figure 6. Bar Chord Forms For Suspended Chords

I make this statement in the exercise section, and I'll repeat it here. If you want to be able to do bar chords readily, you need to practice. BUT -- they can be very hard on your hands and fingers. When you're starting out, trying to do the bar chords, and are practicing the exercises to help you, DO NOT do the exercises daily. Twice a week is fine. And you should usually practice them at the end of your routine. (Your hands and fingers will be cramped and sore after doing them, and you probably won't be able to play very well.) Once you can do bar chords, BE VERY CAREFUL about how often you practice them -- twice a week is probably plenty at first. And again, you should probably practice them at the end of your routine. If you've ever known anyone with carpal tunnel syndrome, you know how debilitating that kind of hand and finger problem can be. Don't cause such problems by over-doing your bar chords, or bar chord exercises. When in doubt, it's better to skip a practice or exercise session, rather than risk problems.
Major Minor Dominant 7th Major 7th Minor 7th Suspended