If you are talking about the various light rail lines and subways in Los Angeles, it is pretty easy. The problem is that each of the lines is separate technology and you have to transfer between each of them. To get from one part of the Los Angeles area to another, such as from the Westside to East Los Angeles through downtown, you can have up to 3 transfers in the downtown area. They are planning to build a connecting line downtown to make it so that you would only have one transfer.
If you are talking about taking the bus, this is a bit more complicated. You just have to do your research and get a copy of the bus schedule.
