How do you call this maneuver in which you put your hands together to act as a support in which someone can climb or step up to reach a higher ground? I hope I was clear enough.
Giving someone a "boost." When getting on a horse it is called a "leg up."
leg up - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.
boost - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.
Thank you, they don't teach you what a leg-up or a boost is in advanced / business English he-he.