Take a deep breath. What engine model? Or what car year and model?
Pull the #1 cylinder spark plug out. Number 1 cylinder on D series engines is the one closest to the timing belt cover, furthest from the distributor. Stick something that's not metal (like two disposable chopsticks taped together) down into the cylinder, and watch them as you slowly rotate the engine's crank with a breaker bar and 17mm socket. When the chopsticks are at their highest (most pushed-out from cylinder), then the crank is at TDC.
I believe that does not guarantee that the camshaft is at TDC though, for it you need to check the markings on the outside of the cam gear.