Drag them in your signature.
and depending on how you want your signature to look set to normal/lighten/screen/color dodge/linear dodge

Any more questions?

It replaces the whole picture.....

From what i've seen my friend do what you need to do is drags it to the places you want and crop it probably.

It should do this (on a new layer above your background layer)

You then select the new picture layer and have it change to screen/lighten/whatever - you can also play with the transparency % and make it 50% transparent etc.

When you download from planet render make sure you sign up or it will have a black background. Make sure they are .png in other words...

Yeah if you drag and drop you can play around to make it blend or w.e. or you can try and delete the BG manually. Also be sure to resize .