To enable SSH access go to System Preferences - Sharing and enable Remote Login.
If you want to access the machine using Screens or another VNC client, you would enable Screen Sharing on the Sharing pane.
This link, while detailing how to access a Mac from a Windows machine, goes into more detail regarding limiting access to certain users, adding a VNC password (in addition to the usual username and password), etc.
Are you talking about screen sharing?
Turn on screen sharing on the Mini, find it in Finder on the other, then click connect & screen sharing.
(Ie what @scotte said, and I just saw)
As I was looking into Jump, it seems that it’s a RDP and VNC client and has their own proprietary protocol called Fluid Remote Desktop. I don’t know much about their protocol but I’d probably stick with VNC as the protocol.
I’ve tried to use this setup for Backblaze backups, but found that my network wasn’t able to reliably copy files to the Mac Mini from my MacBook Pro. Granted the Mac Mini is from 2013/14 (inherited from my mom) and not beefy at all. But it’s hardwired to a router that can get 10 gig connections. I would timeout a lot on backing up (I think I tried rsync but not sure). I did use ssh to check on things and Screens or connect to server via Finder, neither made a difference in speed. I gave up on the whole setup and just hook up my MacBook Pro (2019) to my external drive directly and backup to it while on the network hardwired. It doesn’t do anything for my daughter or wife, but neither of them store anything locally, it’s all in some cloud (iCloud or Google), as do my iDevices and theirs. But I agree with all of the above for connecting. Good luck!