Hi Jade,
Welcome to the site
There is a thread called getting tunisians to the uk - this has all the information as to the paperwork you need to marry - I know the post is really long

!!! but if you can have a read through I think you will feel a bit better as there is a lot of info on there and if have more questions then feel free to ask.
I know it seems all long and drawn out, but hopefully worth it all in the end lol, good luck hun and welcome again x