The doors should be located properly on their tracks.

Try to slide the doors along the tracks.

If they don't slide well, you may need to lubricate the tracks:

Grab a lubricant: olive oil, fish oil, mineral oil, or petroleum jelly.

Apply a small amount of the lubricant to the edge of the rag.

Fit the edge of the rag into the tracks.

Spread the rag throughout the tracks to spread the lubricant.

Slide the closet door along the tracks to spread the lubricant further.