Awhile means “for a short time.” It is one word, and it works like an adverb: it tells you how long something goes on. Sit awhile. We talked awhile. You do not put for in front of it, because that “for” is already built into the word. The stretch of time is short in a human, loose way — a few minutes, perhaps a little longer — not a year, and not a time you would set on a clock. Though actually many native speakers write a while as two words even when they mean this, and in speech you cannot hear any difference at all. Careful writing still keeps awhile for the adverb, and a while for the noun meaning “a period of time,” which can take for: stay for a while. If you can swap in “for a short time,” the one-word awhile will usually fit.