I have no idea what universities I should be looking at?

I'm Year 12 and I don't know how good (or bad) my ability is - how should I know what universities to target?

You need to get an idea of what your predicted grades will be from teachers and mocks.

Ask careers for a look at this book or the library or check in a bookshop. No need to buy.

https://www.amazon.co.uk/HEAP-2018-University-Degree-Course/dp/1911067486/ref=sr_1_fkmr0_1?ie=UTF8&qid=1520118215&sr=8-1-fkmr0&keywords=heap+universtyoffers

Once you have id'd your course that you want to do then the book ranks unis in terms of typical offer grades, so you can match those up with your expected grades and use that as a starting point for unis you might get into. Then you can do further research on the unis n your list.