The right side is the outside of a garment, or the part of a scarf that has the pattern. A garter stitch scarf has no right side or wrong side, and a garter stitch sweater only has a right side/wrong side when you start shaping for where the arms and neck are.
In stockinette, the flat side with the v's is the right side and the purl side is the wrong side. In reverse stockinette, the reverse is true, naturally.
After you cast on, the first row you knit is the first row of the pattern, whether it's the right side or the wrong side. Usually a pattern tells you rs/ws more as a way of orienting you to where you are. As your pattern develops it becomes obvious which is the rs/ws.