Barre chords are a unique type of guitar chord. They are essentially a movable guitar chord. The term barre refers to barring every string at a certain fret with a finger. What I mean by this is taking your index finder and lets say you barre the entire 3rd fret. Every string on the third fret will be pressed down by your index finger allowing the rest of your fingers to be placed wherever they are to be placed for whatever chord you are trying to play. The index finger essentially becomes the movable nut.
Barre chords are referred to as moving chords because you can essentially take any regular minor and major chord and place it anywhere on the guitar by barring the correct frets. This can make for some very interesting and unique sounds and allow the guitarist complete chord freedom.
The difficulty in learning barre chords is the finger muscle and coordination that it requires. While half barre chords are not quite as difficult and are something you should practice before attempting full barre chords. This refers to the index finger not covering every string with one press, but sometimes only two or three strings.
Another difficult aspect of learning barre chords is getting them to be clean. With the amount of finger muscle it takes it can be very difficult to get all of the notes pressed down precisely enough. Keep practicing till you can really make the notes ring. If at any time you feel any amount of pain from practicing this stop and let your fingers rest.
This can be a time consuming process and can be discouraging if you let yourself get down about it. Implement this into your learning routine and not have it be the staple of what you are trying to learn. After a few weeks you will start to get better at it and that clean sound should be coming in. This will be a huge motivation for you to keep pushing.
With all this in mind, look up some barred chords such as Bb Major, B Minor, and F Major and get to practicing!