I've been watching Ethan Becker videos but he says I should never draw with an oval. Then he said I should never draw with a box. What do I do now? Everything I've learned up to this point seems worthless.

https://www.youtube.com/watch?v=FCHhNJWzUnc

https://www.youtube.com/watch?v=7TRlYMqjfIM&t=647s