When you want to change colors, just start knitting with the new color. The ends can be loosely tied, but the stitches will probably remain loose but you can tighten them up. If you change colors after just a few rows you can carry the color you aren't using up the side and avoid all those pesky ends to weave in. If you do this, you might want to cover the edge later with a border of some sort, but that's your call. You could try it out on a small swatch just to get the hang of it; you might have some specific questions that could be addressed before you start a bigger project. It's not difficult, just some things to learn.
You can't knit the left sock first. Ever.