How do we know so much about biochemistry?

Chemists have figured out the structure of some rather complex molecules. How do they figure out the sequencing? How is it determined if a molecule is a ring or if it has a branching structure and how do they know the angles of bonds between adjacent atoms? They can’t just use a microscope to look at the molecules. Just as amazing to me are the details of chemical reactions, like how an enzyme catalyzes a reaction or the rather complex chain of reactions in photosynthesis.