Your goal is to lead your mentees closer or all the way to their goal.
On a high level, you should take care of your mentee and help them to reach their goal. This means to give them advice or even provide connections along the way.
Depending on the services you choose to provide, you might also be expected to give them weekly tasks, challenge projects, to help them debug problems or to hop on a call with them.
In detail, mentees expect reasonable response times, great communication and for you to hold up your part of the deal. If you set your profile to provide a call every other week and the mentee expect to get that.