Evaluating Statements Using a Parse Tree

Question

I'm building a compiler. I already have a parse tree which I built using Bison for a grammar similar to the ANSI C grammar in this link. I see that for multiplicative expression in my parse tree, there can be 3 children e.g.

child 1: multiplicative_expression 
child 2: '*'
child 3: cast_expression

I expect to implement a new class for interpreting the parse tree. However, I have no idea how to even traverse the parse tree in order to evaluate the statements. How do I traverse the tree properly in order to interpret all the types of statements? I want to interpret not only multiplicative statements but also if-else statements etc.