Several factors arise with barre chords. The first consideration for me is the action of the guitar. If that's not good, any player will have hard work making them sound good easily. In a lot of classical playing, half barres are used, and those are easier to play, and get you into the right positions better.
Bear in mind that with full 5 or 6 string barres, there is never the need to actually press down all the strings - two or three are usually pressed down by fingers higher up the fretboard than the barre.
Barres are notoriously difficult to start with - I've only ever had one student who played them cleanly, first time, in the lesson, having only just been introduced to them - certainly not practised beforehand. All others take a few weeks to settle themselves in.
Experiment with rolling the barre finger so that it touches the strings with its more boney side, nearer to the thumb. Also, decide how much finger needs to be sticking out at the top on the fretboard, near the 6th string, so no strings are under the creases of skin where the joints are.
And sort it out with a teacher!