You will need a VPN to netplay with this emulator. Download hamachi or Comodo VPN. Unless you can figure out what ports does this emulator use, there is no other way to play this over the internet besides VPNs.
Beside VBA-Link, it's the only other Game Boy (Classic/Color) emulator that emulates Cable Link
You can trade with yourself
Very simple to use
Resource light, so you can run several instances even on lower-end computers
Has basic chat during netplay
Requires a physical LAN or a VPN to use
Documentation doesn't mention what port does it use to bypass using VPN
Works very well up to 150ms. Anything beyond that is nigh unplayable
Unpack the emulator wherever you want
Configure your emulator: map buttons (physical controller preferred!), change resolutions, apply filters (if you want them)
Go to Options, click Folders
Set a path for your save files and ROMs folders, click OK
Go to File, click Netplay. A window will appear.
In the ROM section, set the ROM you'll be using in the "Player" box, and the ROM your opponent will be using in the "Rival" box (unless you're both using the same ROM).
If you're hosting:
Type in a number between 1024 and 65535 in the Timeout field (1024 usually works just fine)
Click connect and wait
If you're connecting:
Type in your opponent's VPN IP
Click Connect and wait
The status section will change to some other illegible gibberish and a status bar will appear (AFAIK, haven't used it in a very long time so I don't remember)
Once connection has been established, the game will start for both people and a small rudimentary chat box will appear. Enjoy!
Worth noting: the game will be choppy/laggy, and will still be somewhat playable at 150 ms. Anything beyond will respond too slowly to be playable. Be warned.