It’s the Priestly Blessing (although in some Reform synagogues the rabbi will do it rather than calling up all congregants of priestly lineage to do it--i.e. everyone whose last name is Cohen or Katz or Kaplan or whatever is supposed to go up and collectively bless the community together).
The words match the oldest excerpt of the Bible found by archeologists, on amulets in grave goods dating from before the big redaction project that actually produced the Bible in its written forms. (NB: Jewish amulets usually take the form of written text; this is even more true in the modern era.) There is a real sense in which this blessing predates Jewish religion as we usually understand it.
The translation is “May HaShem bless and keep you, may HaShem’s face shine on you and show you favor, may HaShem lift his face to you and give you peace.”
In the Jewish religious context, “may HaShem bless and keep you” means, like, may God decide that you’re going to keep living a while longer. So the benediction literally means Live Long and Prosper in Peace.