To begin the chain make a loop, then pull a loop of yarn through the loop.
Every time that you pull a new loop, pull the yarn snug, this will keep the loop size the same as the hook size. Now if you're going for a looser crochet, than this rule goes straight out the window.
Next, grab another bit of yarn and pull another loop, and another and another. You can buy a stitch counter at a craft store or make check marks on a piece of paper as you go. I've tried it both ways and both work fine.
If you're putting in a row of SC (single crochets) than you need 1 chain - see above where I'm pointing at the 2 chains from the hook. One loop is for the turning chain, the next is where you start.
If you're putting in a row of HDC or DC (half and full double crochet) than you need 2 chains. Above you'll see I skipped 2 chains and am now pointing at the third chain from the hook.