How do you use/play a ship in the sim?
 

What I mean is I have downloaded some playable ships but when I select a mission they don't appear in the list or in a career, some do but what about the ones that don't?

Do I have to create a mission to use them or am I missing something, any help appreciated?

Col.

It could be several things really. If the vessel shows up in the list for some missions but not all, it's the availability date of the vessel. This can be seen in the stock game as well. If the vessel doesn't show up at all it's most likely a double folder issue with the mod. The correct file path for a mod should be MODS/Mod Name/Data. Sometimes you can get MODS/Mod Name/Mod Name/Data and the game won't read it properly.