To install NoMachine on your miniPC,

1) download the package from
I don't know exactly what OS you've installed but I'll assume it's ubuntu on a 64-bit CPU
In that case you'd download "NoMachine for Linux DEB amd64"

2) Put the DEB file on your miniPC.
cd to that directory and type "dpkg -I nomachine_7.6.2_4_amd64.deb"

3) Install the software on the machine you want to use as a client (the one indoors, with a monitor)
Again I don't know what OS you use indoors, but you can install for Win, Mac, linux, iOS, or Android here:

4) Start the client program on your desktop doors. Click "Connection" and choose the miniPC

Let me know if you have trouble!