Where can I read the works of Timely Comics and Atlas Comics before they became Marvel Comics?

I finished reading about Iron Man, but the book said something about comics from two other former companies that ultimately became the one we know well today, including the old and classic Captain America comics back then.

Does anybody know where I can read about this?

I use Hoopla, but they don’t have it and your answers may vary depending on your input.

I may also use Nook by Barnes & Noble.