Read section 11.3 and then do Exercise 187. As always, make sure that you write check-expects, a signature, and a description before writing your function.
Read section 11.4, then do Exercise 193.
Read section 12.4 (you also need to read the description of the arrangements function in section 12.3).
Then do exercises 212 and 213. Note that the function you are designing in 213 needs several helper functions. Pay close attention to examples and signatures. Keep in mind that your tests may fail not because of a wrong result, but because of a differnt order of elements, so don't just rely on check-expects, check your results manually as well.
Caution: this is a challenging problem. Think carefully of what functions you need; design them one-by-one; use paper and pencil to work through examples. Start early and ask questions.