im having trouble finding waterfall do you know i place i can get one if you do can you post a link im having trouble understanding TheGhost's tutorial since im new but if you cant what tools do i need to do what the tutorial said?

you need to make it.
the best way for you to learn how to do it is read the official hek tutorial.
http://hce.halomaps.org/hek/
if you are happy you know everything else it covers then click on the section named
level creation-part 2 then scroll down to
(The following steps and example images will demonstrate the modification of the terrain to create a stream bed).
that will explain it all.

Also you may want to try creating a waterfall using the particle system. Sometimes creating a model one to use doesnt work out. If you want to.try, try using a stock effect tag first and play around with the emitter settings and bitmaps. A lot of great Halo 2 waterfall items were made with this method.