is an interjunction, meaning 'well then, (...)'
さて、そろそろ出ますか。 Well then, let's slowly get leaving.
さて、とりあえず乾杯しましょう。 Well then, first of all let's have a toast!
さて、この問題をこたえが分かる人は居ますか？ Well then, is there any here who understands the answer to this question?