Ohhhhhhhhhh-I got you boo! You're going to design one costume for each of the named characters-that being said, there's a lot in Into The Woods so I would narrow it down and just pick 5-I would go with the main characters, since you'll have the most to go off of...
Anything you want-but for me when I costume design, I like to draw it traditionally-you can take a picture of the drawings and hand them in. I can also help you with the process if you want, cuz I've done it multiple times now.
Oh no I ain't helping you with the actual designs-that's on you-but I can tell you the process-cuz you legit don't know how to do it and that puts you at a disadvantage.
Okie doke-so firstly you're gonna wanna read through the script-when you do this, annotate. Look for if there's any actual things in the script it specificly says you need costume wise-also look at themes in the text. Yes I know this sounds like english homework but trust me.