May I just mention something that may or may not affect you?
If your Mother's iPhone was linked at an Apple ID - presumably hers - it would be advisable to disassociate that Apple ID. In other words, for her to sign out of her Apple ID and "Find My Phone". Indeed, ideally, she (or you on her behalf) should reset the iPhone having done the aforementioned so that you are using the iPhone as if new. Otherwise, Apple thinks it's still hers.
This way, you can set it up in your name with your preferences and you can purchase music through iTunes - all associated with your Apple ID. As this is your first iPhone, you would need to create one if you've never had one before.
The danger of not taking these steps is that you may not be able to purchase music or use the iPhone in "your" way because it would still be locked into your Mother's Apple ID. This can cause major difficulties.
Need more specific advice on this, please ask. That is what we are here for.
Ian