An introduction to Set Theory is found in Chapter 1, Section 1.2 in the Epp textbook or Section 0.3 in the Levin textbook . This material was all covered in Inf1A and you should find that you know all the concepts. The video can also give you a quick recap.
To test your understanding you can try the following questions in Epp.
- Exercise 1.2, Questions 1, 3, 9, and 11
Or you could try some questions online from Levin