What do you want to know? Component snap is used to automatically place components. There are two settings that relate to this. The first is in your config.pro file. The setting is comp_snap_dist_tolerance (0.5 my setting) this sets the snapping tolerance.
The second is in the component placement dialog box. Select preferences then expand snap if it is not already expanded. There is an option, activate snapping, check this box.
To use it upon component placement the part will need to be in the assembly window while you are constraining it. Select a mate, align etc.. either on the part or the assembly then use Ctrl & Alt to move your component. As you move it various possible references are shown. When you are happy with one release Ctrl & Alt then your part will be constrained. This takes a bit of getting used to.
If you can't understand this or need more help let me know.
Good Luck