Setup External Acces

Hi

First off English is not my first language is I will apologies for multiple grammar mistakes in advance.

I have been struggling with setting up Rockstor NAS for a couple of days now. And now i have finally found my ways to the forums i am usually to block headed to go there. I have a file server up and running right now and I can access data and write to it via my own LAN. But i would really like to set up my NAS for external use so that when I am on school I can access it from there. Now i have been reading on the subject and it should be possible to do using SFTP and port forwarding port 80 and 22. But i don’t know what to do after that and I can’t find much on the forums and internet. I did read a post about External Access on this forum about VPNing to the NAS if that could work it would be fine too.If someone knows how to fix this it would be AWESOME