To get started with LaTex quickly I googled a bit and quickly found a cross-platform editor I am very happy with – TexMaker.
You can install it by issuing:
sudo apt-get install texmaker
The interface is very intuitive. Among the editor’s features are code completion, spell-checker (although I didn’t succed at configuring it), wizards with document templates… You can find the user manual and a decent LaTex reference under Help. You can see what it looks like in this screenshot:
All in all a very smooth editor, great to work with!
If you don’t know LaTex, to get you started here is some sample code I just wrote today: