How do I open up my Mac to remote sharing anywhere? I've been looking around and I can only find a way to access my iMac and it's files on a local network. But if I'm away or at school, this kinda puts a hold on my work and is mighty inconvenient. If anyone could tell me how or point me towards resources, that'd be great!

In specifics, I'd like to use my iPhone (jailbroken, iOS 12.1) to be able to ssh, scp, or sftp from school.
I would recommend the screens app and screens connect. The software is not only fast and works excellently, but it helps diagnose if your network conditions are not correct to accept incoming traffic past any firewalls or NAT borders. 


https://edovia.com/en/


For ssh, I use prompt and recommend that as well. 


https://www.panic.com/prompt/


Together they solve all issues like not knowing your IP address of your router or having to set up dynamic DNS.