TSH measures the amount of the thyroid stimulating hormone(TSH) in your blood. This can tell you if you have hyperthyroidism(too much thyroid hormone) or hypothyroidism(too little thyroid hormone). This test does not show you what is causing the problem.
Free T4(thyroxine) is a hormone produced by your thyroid that flows through your bloodstream independently.
Free T3(triiodothyronine) is a hormone produced by your thyroid that flow your bloodstream independently.