Mechanics is tricky at first, there are loads of formulas to get your head around, it's where you'll get yourself up to the standards required at A Level. You'll have to handle large amounts of data at once, converting units, and rearranging complex formula.
The first thing to get your head around is all the SI units and their prefixes and suffixes. Then you'll probably get used to using the equations of linear motion, (or the suvat equations as they are commonly called.)
You'll learn a whole load of the dynamics, which is how forces cause or alter motion. It'll get tricky here as you need to work in two dimensions, including using trigonometry. Then you'll be putting it all together and learning how objects move under gravity in projectile motion.
Practice loads, learn the tricks and you'll do really well. Some videos to get you started on this page.