As a brief explanation, 1 foot pound means a 1 pound weight hung 1 foot from the bolt. So for a 20 foot pound torque setting, you could hang a 10 pound weight 2 feet from the bolt or a 20 pound weight 1 foot etc.
Most torque wrenches are pretty accurate these days, you only need to spend silly money if you are using them every day for critical applications such as cylinder head bolts on all alloy engines.