All I have to do is submit my piece of work in this thread, right? And I am allowed to just make up an alien species, correct? I'm not even sure if Starfleet will be in it. I don't know yet where this is going. Does it have to have established lore in it?
pointed out, you have to post your fic in a separate thread and a link to it here in this one.
Your story should take place in the Trekverse but Starfleet doesn't have to be in it. Original characters and original aliens are perfectly all right.