normal maps and baking?

in a few videos i have seen normal maps

but i donth now what they are and what they do.:confused:
there are no good tutorials on youtube so i ask it here.

what are normal maps?

A starting point.
They fake the look that your object has more 3 dimensional detail than it really has. You can then have a low polygon model that looks like a high polygon model, useful for in game models and faster rendering. If you use a displacement map it actually does displace your geometry so for high detail you need very high resolution mesh.
A mix of displacement map to give low detail displacement in combination with a normal map to give high details can be used to give the benefits of both methods.

ok i tink it was someting like the displace modefier

and thanks
i gona use this