how could i get into maths as a hobby?

in only in highschool and i really really enjoy maths and i really want to get into it as a hobby but i dont know where to start. people tell me to read up on theories and stuff but i barely understand anything at all. i am studying advanced maths past my age as i am completing my maths a level during my gcses but i want to go beyond that and i still dont really know much and when i look at people talk on this subreddit ik that there are a lot of adults here but i feel so behind in maths😭. i want to start at a basic level, but not somewhere too basic. i just cant find an in between or where to begin. does anyone have any tips?