(sorry for the late reply) Custom ROMs are something else and are in no way necessary for rooting the phone. You can totally root your phone with Magisk while staying on your manufacturer's ROM, or flash (install) a custom ROM without rooting the phone and not being locked from anything your Android phone can already do. But you won't have full access to your phone if you don't root and will eventually need at least some degree of power over it, which is why most people root their phone too. But custom ROMs alone are also great, you can check if there are good ones (or if there are any) on xda-developers by searching your phone on it. But be careful and follow the instruction to the letter: you won't be able to blame anybody for bricking your phone (look for hard brick and soft brick) as all authors clearly state they're in no way responsible if you fuck up something and your phone doesn't work anymore. The best thing to do as a beginner is to search deeply on the internet for days if not weeks in order to feel more confident and more importantly understand what is a ROM, what is a recovery (TWRP being the main one), a bootloader, etc, so you know what you're going to do.