Open MatterControl and click the "Printers..." button and then click on the Add New Printer button.

You'll be presented with a Setup Wizard that will allow you to enter the Make & Model of the printer you're adding. In this case, you'll chose the one that best describes your printer.

Note that if you're using the SeeMeCNC branded version of MatterControl, SeeMeCNC will be the only Make available.

If you have an H2 printer, it has not yet been added to MatterControl as an option. Choose Orion instead. You will need to change the bed size in the Printer > Print Area settings of MatterControl.

For the 178mm arms your bed size is: 140 x 140

For the 290mm arms your bed size is: 200 x 200

The next page of the Setup Wizard will ask to install a Communications Driver. If you installed one during the MatterControl install process, you don't need to install a driver here. For Mac & Linux users, no driver is required.