In short, ARGB can show different colors at the same time, and RGB can't show different colors at the same time.
For example, a ARGB Fan spinning can show Purple and Blue at the same time like a light show.
A RGB Fan would only show Purple first, fade away, then show Blue.
Pictured Examples:
ARGB Fan
View: https://imgur.com/xNOmWeB
RGB Fan
View: https://imgur.com/koFtEJd
The MPG 2390 Gaming Plus only has 2 RGB Headers with no A-RGB Headers, so you would have to buy a RGB Controller if you want to control the LED's. Being powered by the USB Header on your motherboard.
Something like this would work
https://www.coolermaster.com/catalog/coolers/rgb-accessories/rgb-led-controller/#Video
After you connect it, control it through Coolermaster's own RGB Software.
NOTE: I don't really work with MSI Boards, but for their Gaming Plus Series mostly do not support Mystic Light so I don't know how you would control the RGB on that motherboard other than using a Controller. Even when there are 2 RGB Headers on there...