create a gexf file?

[Scilens]

Hi!
I'm new to using gexf, so please be patient = )
I have a gexf file that I've been working with, and I tried to get some other data into the same format. So I wrote a script that basically creates a .txt file that looks exactly like the other .gexf file (except that the nodes and edges are different. but the structure and everything is the same). Now how do I convert that to a .gexf file? Just saving it as .gexf didn't work, and I didn't figure out how to use Gephi for that (if it's possible at all).
I also googled and tried a few things, but I haven't found anything to help me. What I basically need to know is how to create a .gexf file that I want to write from scratch (not extract from any data or anything)