What does this mean if this red light comes on

[candid crest]

Impossible for us to answer without knowing the exact make and model of motherboard in your PC.

[quick marlin]

B760M DS3H AX DDR4

[candid crest]

That's just a model, so guessing it's a Gigabyte motherboard... anywho, the user manual (page 4) makes no mention of an LED light in that location so you'll have to see if something is silkscreen printed onto the motherboard beside that LED light.
https://www.gigabyte.com/Motherboard/B760M-DS3H-AX-DDR4-rev-1x/support#support-manual

[quick marlin]

i’m js gonna go get it checked up

but what is the best cpu for this motherboard

?

[quick marlin]

?

[candid crest]

Best is subjective to your workload, but objectively it'll be the first one on this list.
https://www.gigabyte.com/Motherboard/B760M-DS3H-AX-DDR4-rev-1x/support#support-cpu

[quick marlin]

on what list ?