When you work from a chart, read the right side rows from right to left and the wrong side rows from left to right. If you were working in the round, all rows are read right to left.
All charts do have a key. One thing to remember though, that most of the time, empty squares are really stockinette stitch--knit on the right side and purl on the wrong side. After a while you get to know what your pattern is supposed to look like so it makes it a lot easier.
I like to keep track of charts by blocking out all the rows above the one I'm working on with post it notes. It really helps.