So this is more of a generic question. I seem to keep finding myself being put on larger and larger projects. Recently I have been assigned to a very large project written in C and VHDL. The goal is for me to become familiar with the code and eventually take the lead on the project. This is by far the largest project I have been assigned to work on that I didn't start.

So here is my question: What methods/tools do you use to learn how everything works?

Do you just increase and expand on comments?
Do you make a UML representation of the project?

Any tips would be great! Thanks