If people can read them everything on wikipedia or search google, then what the f**k these forums are wasting bandwidth for? Some times people need short but to the point answers which can't be find on wikipedia or google-search.
To OP, here some brief explanation of few game settings -
vSync - Vertical Synchronization. It synchronizes your FPS with your monitor's refresh rate. Otherwise the pictures (either games or videos) will show some effects known as 'tearing' or 'disjointed image'.
If you use VSync, you will lock your FPS to your monitor refresh rate. The thing is if you have it off, your GPU can render as many frames as it can before your monitor refreshes.
So, if you have high-end refresh rate (100 Hz!) with high-end GPU, then turning vsync on may help you but don't turn it on with low-end GPU. If you have somewhat mid-range (75Hz of less) monitor, leave vSync as off.
OpenGL or Direct3D are two graphics API for rendering. there are many settings related to these API. Be specific.