BMW, when you do a scarf, you will generally use a stitch like ribbing, or garter, or basketweave, or some kind of lace, that is reversible--looks the same on both sides. In that case, there isn't a "right" side because they are both the same. In Stockinette stitch, where you knit a row, then purl a row, the knit side (V) is the right side and the purl side (bump) is the wrong side--but that's more so for sweaters, sleeves, bags, gloves etc, and really should be referred to as "inside" and "outside" instead of right and wrong (IMHO---let's start a revolution!!!)
If you are K-ing and P-ing in the same row to create a pattern like a letter, the side where the shape is backwards is the inside/wrong side. If you're doing a symetrical shape, like a heart, star, moon, clover, horseshoe, then the shape will be the same on both sides, but you'll see that the shape "pops out" on one side, and "sinks in" on the other. If the pattern doesn't tell you which side is the right side, you get to pick
I think I understand you're 2nd question--I had this question too when i was first starting. When your right needle is empty, and you're about to work the stitches on your left needle, the rows that are complete should be coming towards you... that is, if you hold the left needle straight up and down (point up) the "hangy" will be on the right side of the left needle. The left side of the left needle will just show the loops of each stitch around the needle. If you hold the left needle parallel to the ground, with the ppoint on the right and the end of the needle on the left, your stithes will all be hanging down, and the loops going around the needle will be on top.
For your third question, if you're knitting something like a bag that has 300 rows of stockinette stitch, or whatever you're doing where you need to keep track of rows, but don't want to count each one of a large number, you can buy these hangy stitch marker things and hang them on a stitch every 10 rows: they can be hung on the needle, too, but they're geat for marking individual stitches too. I call them the padlock style markers (can I FIND a picture? no! Sheesh!)
Hope that helps!!!