How to make an animation of light in After effects?
Well, there's a lot that would go into that effect, especially if the girl's hand is moving. Here's the basics so that you can better know what kinds of tutorials to search for.

To create the light you'd probably use what's called a "particle generator" combined with a star glow or shine effect (e.g., Trapcode Starglow.) If you don't want to shell out for that plugin, search for how to do "light streaks effect" or "shine effects" in AE "without plugins."

To make it look like it's within her hand (i.e., sandwiched between her fingers and her palm) you'd need to understand how to "animate mask paths" (in order to mask her fingers into their own separate layer.)

To make the light follow her hand around you'd need to learn about "motion tracking."