What do you mean by squeezing all the grapes in it?

Squeezing all the grapes into it means squeezing the grapes into fruit. Grape is a woody vine of Vitaceae, with cylindrical branchlets, longitudinal edges, glabrous or sparse leaves, dense or scattered panicles, well-developed branches at the base, spherical or oval fruits, which bloom in April-May and bear fruit in August-September.