How do you play guitar barre chords?

It is just a dexterity issue. When you first started learning open chords you probably had the same issue. Now that you are trying to make barre chords your hand is in a more restricted position because of having to keep that first finger down. It will come with practice, but think about keeping the hand more open (the palm further away from the fretboard) so you can get those fingers coming in straight, perpendicular to the strings, which will keep you from muting the strings. It will take time. I remember the first time I was shown barre chords, I swore that I could never do it, now I just laugh when I think about that. It will come with time, I promise.