If you still don't understand, make a note of that. When assignments are corrected, mark the problems you missed. Don't erase your work. If you make corrections in class, label them so you will recall that this was done with help. Then try them again later by yourself.
Homework is work done outside of class.
Some instructors ask that it be turned in. Others expect that you do it, correct it, and use it for a study guide. All instructors of mathematics expect you to do it. If your homework is to be turned in, there may be a special form to follow. The trail you leave will be most helpful in determining what went wrong with the problems you were unable to solve.