The Grid 3 is a commonly used piece of software for AAC. Follow the steps below to add commands to your gridset
Gridset quick start Want a headstart? Download a Gridset here. It has all the commands you should need. (You'll need to download the raw file) Just copy/paste and adapt
Use the relaykeys-cli-win.exe with the keypress:LETTER argument (where letter is the key you want to send)
Use the "Copy" command followed by the relaykeys-cli-win.exe paste argument