in cod 4 radiant there is a tool to work terrain, make a crater and so on, how do i do it with hammer?

Luckly there is one in hammer as well. Open the texture select window by pressing shift + A (i think) then make all faces of the brush no draw, next click the displacement tab and click create, then select a power (i normally use 4) then click ok. Next click paint hight and you should have an edit terrain window then use a left click to raise the terrain and a right click to lower it. There is a video tutorial here that goes into more detail and tells you how to use the advanced settings.