#Isaac went up from there to Beersheba

Here "went up" is probably a reference to going north. State in the most natural way for your language that he departed. AT: "Isaac left there and went to Beersheba"

#multiply your descendants

"will cause your descendants to increase greatly" or "will cause your descendants to be very many"

#for my servant Abraham's sake

"for my servant Abraham." AT: You can make the full meaning explicit. AT: "because I promised my servant Abraham that I would do this" (See: [[:en:ta:vol1:translate:figs_explicit]])

#Isaac built an altar there

Why Isaac built an altar can be made explicit. AT: "Isaac built an altar there to sacrifice to Yahweh" (See: [[:en:ta:vol1:translate:figs_explicit]])

#called on the name of Yahweh

Here "name" stands for Yahweh. To "call on" means to pray or to worship. AT: "prayed to Yahweh" or "worshiped Yahweh" (See: [[:en:ta:vol2:translate:figs_metonymy]])