Standard Marlin compatible G-codes can be found at the RepRap wiki: G-code.
Not all standard G-code are supported by the MP Select Mini.
See the Extended G-code Table for G-code that is more or less specific to the MP Select Mini & Malyan printers.
There are a few ways to send G-code commands to the printer. This page will not go into detail on how to use these methods but should be enough to point you in the right direction.
Sending G-code over USB is not the only way to send G-code but is probably the easiest. Many slicer programs have the ability to send G-code to the printer via USB. See your slicer documentation for this feature.
Programs like Printrun (Pronterface) and Repetier-Host are easy to use and don't require much set up. There are precompiled versions of Printrun for Windows that can be used without installation and only require selecting the correct COM port to connect to the printer.
G-code can be sent to the printer by saving the commands to a .gcode file. Copy the .gcode onto a microSD card and select the file from the Print menu.
While the MP Select Mini V1/V2 is connected to WiFi you may use the format
http://PRINTERS_IP_ADDRESS/set?code=G-CODE_COMMAND to send a single line of code g-code using a web browsers address/URL bar. See the examples in the following code block.
http://192.168.20.113/set?code=G1 X53 http://192.168.20.113/set?code=M563 S6 http://192.168.20.113/set?code=G1 X Y
When a command is sent and received successfully the browser should display `Ok`, `OK`, or `ok`. Additional g-code commands can be sent one after another using the same format.