These are the proportions of the hand.
Draw ellipsed to make room for the fingers, otherwise they don’t fit sometimes.
Fingers fold in when they bend.
Look at your own hand, or a photo of a hand, and break the hand down into the shapes of the manikin.
Look at your hand, or a reference photo, put it away and draw from memory. Use the reference to fix mistakes in the drawing. Repeat until it comes out okay.