To get garter stitch in the round, you repeat knit 1 round, purl 1 round, etc.
What is it exactly that you need to know about cable charts? A pattern will nearly always have a legend so you know what the symbols are. If you are knitting flat, you will generally start at the bottom right hand corner of the chart and work right to left for odd numbered rows, and left to right for even numbered rows. If you are working in the round the chart will be read from the lower right hand corner as well, but every row is read right to left because when you are working in the round, every row is a right side row.