If you want to get started with fundamentals I would highly recommend starting with Fundamentals of Figure Drawing it will help you develop a good understanding of Form and basic Perspective. For a good introduction to perspective, Marshall has a 12 video course on his website.(https://marshallart.com/SHOP/all-products/all-videos/1994-perspective-drawing-series/) Otherwise you could learn a lot from ModernDayJames's Perspective Series on Youtube.(https://www.youtube.com/playlist?list=PL-YQfqQQpg3dFq5rxS9eFFf2ksMb7Ygpq) If you want to learn how to use primitive shapes to indicate form and draw almost anything with a bit of introduction to design, Concept Design Academy has Dynamic Sketching which i found to be extremely helpful. Composition and Values are the next step after form and perspective. For light and shadow - Dorian Iten's Course is the best one I know of. For composition - (I haven't personally gone through this one) Bill Perkin's Course on NMA is very comprehensive But for a brief introduction check out (https://www.youtube.com/watch?v=wg-So3ElA8g) I hope you find this helpful.

Hello! Well if you are interested in characters, and figure drawing then do the Figure Drawing Fundamentals course, if you want to do portraits, then the Portrait Drawing Fundamentals :)