You can use Brickset to find part numbers, using the search bar in the top-right corner.

thanks

I am new and looking for a flat 2x2 brick, but I don't know how to find it, because I don't know what to name it.

Search 2x2 using the bar above the list of parts, on the right side of your screen. You can also use the filter button to turn off decorated parts, so that it's easier to look through the results.

Thanks a lot.