Same as a regular charge but you only get a single move, not a double. It's listed in the PHB table that gives partial actions. Since it's a partial action, you can normally only perform it was a readied action or in the surprise round. While the Sage has said that all movement in the round must be in the same direction like a normal charge, though many people have decided to allow the character to partial charge in a different direction from the prior movement.
IceBear