I dont get that tool.

The one where you make curved edges.

It keeps on cutting something whenever I press enter!

I dont want to make it cut

I just want to seperate a wall!

how?

I did it before

But I dont know how!

http://developer.valvesoftware.com/wiki ... pping_Tool

Click on the icon until the entire object is white.

I assume you mean the Clip too? You draw your lines with it in the 2D windows, then press Enter to make the clip. Clicking the icon changes the mode - left clip, right clip, and "split" where nothing is removed, and things are just clipped in half.

To clip a wall in half, just draw the horizontal/vertical line, go into Split mode, and perform the clip.

Press shift + x to cycle through which type of cut (ie. red bit cut, then move red bit OTHER side of line, then white so nothing gets cut, just a split)