You cannot wear white, but it can have white on it.
Where is it?
Church? Park? Beach?
What season is it?
If they are fine with you wearing what you want (eg, dress, men or women clothing) maybe go shopping in order - Dress, pant suit (not really a fan for weddings, just try a play suit or even jump suit), then look into more unisex then finally menish.
Make up, go light, natural, hair, GET IT DONE, nails basic colours.
If you have time, go shopping for a dress to see how they look on you, you never know.
Play suits & jump suits are a much better look than a pant suit though