1st level, 2nd level, Tertiary, and Quaternary.
The first level is just the different protein groups forming peptide bonds to create a polypeptide
The second level consists of hydrogen bonds between the H and the O molecules in the proteins forming pleated and helical shapes
The Tertiary structure is the interactions of different R groups binding to each other (many different types of bonds happen between the R groups)
The Quaternary structure is many polypeptides interacting with each other