Hello and congratulations on your engagement and wedding to come!
What do you know about diamonds in general? Other than the fact that they are very beautiful stones and are chosen by very many people for all sorts of reasons and for all kinds of jewellery items, not many people know too much about these precious stones.
I used to work for a jewellery store where we ran training courses for our customers so that they could make their purchases knowledgably (preferably from us of course) but from anywhere they wished.
What do you know about CUT or CLARITY or COLOUR or CARATs?
I found a very nice site that summarises all of this for you
www.myjewglerysource.com that you may like to visit but there are many other sites too which speak of the same subject.
Please note that I have nothing to do with this site and that I do not profit at all from telling you about them, it is put here just to help you and I found the information they offer clearly presented.
Anyway, my best advice is DO NOT buy your diamond ring online. Just don't. If a jewellery store is advertising their jewellery and the rings are fully described in terms of the four Cs above, then choose, get an idea of costs etc. BUT go to the store to "see with you fingers" and try on the ring. You will be very pleased that you did, no matter what your budget.
Good luck!