Depending on how many stitches you have cast on you will either end by knitting two or purling two; so if you have cast on 20 stitches you will end with two purl stitches 22 two knit stitches and so on. If you ended on two purls then you will begin the reverse side with two knit stitches and vice versa. Look at your knitting and it will tell you what to do, knit stitches look like "V"s and purl stitches "-"s, knit (purl) what you see.
Here are a few good illustrations:
Ps. Kacyann you might also want to post or move your query to the "How to Section" of the group where more people can respond to your question properly.