Read about it in the textbook, here: Chapter 7.2
Video links – all these videos are closed captioned, so you can listen or watch without the sound.
7.2 Video a. Adding and subtracting rational (fractional) expressions with the same denominator — a good way to start understanding before going to the next video!
7.2 Video b. Adding and subtracting rational expressions with different denominators — starts with numbers, then goes on to variables and trinomials.
7.3 Video c. Adding and subtracting rational expressions with different, monomial denominators and then writing the domain.
7.3 Video d. Adding and subtracting three rational expressions (two binomials and a trinomial).
7.3 Video e. Simplifying complex fractions by flipping and dividing.
7.3 Video f. Simplifying complex fractions by multiplying everything by a common denominator (lcd), several examples. And also, here. Caution: ads!
Open Access College Algebra and Trigonometry, 1st Edition 