I've been trying to play bar chords for awhile now using my index finger but i can't master it. Is there any techniques or certain strings i should use? I'd appreciate any help.. thanks

Barre (note correct spelling) chords usually take time (a few months or so at least). The best advice I can give you is to be patient.

The barre across all six strings is called the grande barre. You might practice other barres as well. One of the easist is the barre across the first three strings that makes (on it own) a minor triad.