They are supposedly extending their hands in prayer (assisting whoever might be pronouncing the prayer). It was done frequently in the Charismatic Renewal. They are "helping," so to speak. I don't know how appropriate or licit it might be. Some speakers (priests or otherwise) invite the congregation to add their prayers in this manner.
Kneeling, folding their hands and bowing their heads like Sister Mary Attila said do isn’t good enough for them?
They are extending their hands in a blessing of some sort, which I do not believe they are supposed to be doing, but which occurs at pretty much every parish.