Hi there..U3 and U6 are practicals.. U3 is AS Practicals. U6 is for A2. You can get a small book containing detailed information about conducting those practicals but you have to buy them seperately as they are made for AS and A2. i'm sure you can find them if you google around a bit as i can't seem to remember the exact titles of the books atm.
This is only if you are sitting the written practical papers. If you are not an international student your school teacher would plan something out for you.
UsuallyInternational students sitting these papers go through all the past papers as the current syllabi has been around since 2009 so there are exactly 14 or 15 if you include the current 2016 june one. I'm aware they are currently planning on changing the syllabi but i don't nearly know enough about them to answer any Q. about them.