There are three things that matter in electricity, understanding electrostatics, that's like positive and negative, attraction and repulsion. Understanding Ohm's Law... so that's defining voltage, current and resistance. And finally Understanding Kirchoff's Laws, so that's how circuits behave. I you can get all that right you'll be absolutely golden and do really well in these topics.
Tricky thing is though, those aren't easy concepts to get your head around and the explain a huge number of contexts and phenomena!
Electricity | GCSE