Hi and welcome. Oolite has indeed been designed to be fully moddable. To get you going with OXPs (Oolite eXpansion Packs), start from the wiki pages here: http://wiki.alioth.net/index.php/OXP_howto
. Take note that there is plenty of reading to do and that is because almost everything in the game can be changed. You can add ships, create new graphics, new effects, new HUDs, new weapons (offensive or defensive, with own stats if you so wish), new sounds and music, new AI for ships, new UI, change the way space and planets look, script missions and events if you want and even modify core functionality to a point where an entire new game has been created. There is plenty of information to absorb, but you can of course start by focusing on the area you are interested in and you can ask questions here if things get tricky.