I did corporate training for an international company for about 20 years. Once when I was in Mexico something happened in class and I said something was okay and used my finger and thumb to make the okay sign. They kind of laughed and started talking among themselves. I guess the okay sign means asshole in Mexico so when they explained that I laughed with them and said I didn't know that. One of the jokers in class said "yeah, okay we believe you" and gave me the okay sign. lol

Antropólogy PhD thesis: the meanings and nuance of the word "fine"

You may raise the index finger vertically, but not horizontally; unless you're referring to the thing it is aimed at, so long as it's not a person, unless you're indicating that person directly or making an accusatory statement directed at them, unless the person you are accusing is in a superior tactical and/or strategic position.

The pinky (last) finger is mostly irrelevant.

I'm a bit out of the loop. What social media (or forum) platform is pictured here?

It's really efficient