Penny - on a tablet or PC, go to
https://xiaomi-mi.co.uk/home/user-manuals/ and you will find a complete list of user guides for all Xiaomi/Redmi products.
Check which model of phone you have (it'll be on the box it came in) and scroll down the page quite a long way, past the air conditioners, fan heaters and what all until you come to a section titled "User Guides for Xiaomi Smartphones". Click on your model name and you will download a user guide which you can save and refer to anytime you are baffled by your phone!
I've no idea which model you have but I just downloaded the very top one to see what it looked like and it seems nice and clear, well laid out and not too much mangled English.
Obvs, the first thing you'll need to do is charge it - charger should have been supplied? Then switch it on -the power button on most Android phones is one of the ones on the right side as you look at the screen, could be top or bottom one.
I've never used a Redmi and all phones and versions of Android have their little differences but follow the user guide and, honestly, you'll soon get the hang of it and wonder how on earth you managed without for so long. It's not just phone calls; it's almost a life support system. A calendar to remind you of things you'd probably forget; a camera for when something is happening NOW; maps for when you're lost in a strange town; a calculator to check figures on the hoof; all sorts of useful apps available to check when your bus is due or if your train is cancelled and loads of games you can download to play while you're waiting for that bus or for OH to come out of the bathroom ...
Good luck!