TDC (Top Dead Center): The "0" mark on the crankshaft pulley should be aligned with the notch on the timing belt cover.
4BTDC (Before Top Dead Center): There is a small notch, or mark on the crankshaft pulley that is at the 1 o'clock position when viewed from the front of the vehicle. This mark should be aligned with the pointer on the timing belt cover.
There is also a timing mark on the camshaft sprocket, which is a small "V" mark. This mark should be aligned with the pointer on the timing belt cover.
It's important to make sure that all of the timing marks are correctly aligned before starting the engine, as incorrect timing can cause engine damage.