What does the hand gesture mean when people have their index and thumb making a circle and the other 3 fingers are straight and all together?

It means OK. IF I said, "Pick up some groceries for me at the store", and the person made that jesture, it would mean he understood and will pick up the groceries.

depends on how they turn the hand and move it. Showing you the O means OK. Flipping the three fingers up at you means to go screw yourself.

everything fine and ok.

In some countries, making that gesture is a way of saying "You're an anus". Yahoo won't let me write the word that would generally replace "anus"

In my country, Taiwan, here, this hand gesture has the same meaning as you have in America.

This gesture is used in many parts of the world and it means different things in different places. In some places, it's an extremely vulgar gesture. In other places, such as the US, it generally means All is well, all is okay. Or, as GA41 said, I understand and will comply.

He could be referee in a sporting event, signaling time in, start the time clock.

They're playing the world's smallest fiddle for you which means they don't sympathize with you at all.