If I had any tips to start the first would be to keep drawing stuff.
Draw whatever floats your boat and fill sketchbooks.
If you keep them you'll be able to look back and see how much you improve.
You WILL improve.
Get inspired. Start some Pinterest boards and fill them with what you like and figure out what it is about them that appeals to you.
Try and get hold of some design packages even if they're the free ones and start making things to get used to how they work and get an understanding of composition, colour and layout.
Re-create/copy some simple things that you like, maybe a logo or something.
Set yourself some projects. things that interest you is a good start.
When you're ready, start sharing them to get feedback and advice.
Its sometimes hard to take criticism but you'll learn from it and you need broad shoulders in design.
Also, as i have to choose a levels next year my mum said i should start looking into job shadowing and experience. Do you know how i should go
about that and if large companies would allow me to job shadow like google
It's really quite hard for even people at Uni to secure an internship of any kind.
My niece spent ages trying and had to move to London for a while for hers and it cost her parents a fortune.
The competition to get in at somewhere like Google is incredible.
Even getting a work placement in design whilst at school or college can be very difficult and much of the time you're expected to just make tea or do menial (non-design) duties.
When I was at college I ended up working at a print finishers which it just repetitive, factory type work and printing t-shirts.
That being said, don't think you can't do it. It's just really difficult.
When I used to work in publishing they'd send me the work experience kids as they couldn't be bothered with them and I'd do my level best to make sure they did some 'real' design and learned something about working in design.
Working in design of any kind can be very difficult to start with.
Many, many people simply just give up.
It's the ones that love it and are determined that succeed.