Barre chords are often ver had at first. An idea is to take an open E major chord, switch 1st for 2nd finger, 2nd for 3rd, and 3rd for 4th, and practice with this position to help get used to the position of a 6th string major barre chord.
Also, try barring the index finger on its own, even before you start working on barre chords. Don't worry if not all the strings sound clear. In the case of 6th string chords, only the 6th, 1st and 2nd need to sound clear (the 3rd string also in the case of 6th string minor barre chords).