Glink uses the standard Android on-screen keyboard. The keyboard settings and are found in the Android settings app in the Language & input section.
The keyboard can be configured to always be up from the main Glink screen in Menu > General options.
Glink is initially set up with default keyboard mapping when using device keypad or external Bluetooth keyboard, see Keyboard shortcuts for a list.
Device buttons and keys can be remapped, select Settings->Keyboard and then see Keyboard mappings button.