You can use any real 6-string guitar with Yousician, be it acoustic, electric or electroacoustic.
Setting up an electric or electroacoustics guitar is described below.
Plug your guitar in.
After you plug in using a USB guitar adapter, you need to change the input device (you can change it in Game settings)
If your audio input device does not show up in the game settings menu, please check the "Audio MIDI setup" of your computer. Also make sure to put some volume to the guitar. You can see if it works by observing the MIC / VU meter while playing on the guitar (in the tuner screen).
Read more about setting up an electric guitar here.