remotely accessing another computer

My mother just got an iMAC and is switching from windows. I want to be able to log into her computer and help her with set up remotely (I'm on the east coast she's on the west)... Can anyone tell me what we need to do? I want to be able to access her screen and files to help set up email, face time, messages, etc. I have read so many different suggestions and am confused as how to go about this.

We are both on Mojave.

Thank you.