Usually you notice foxtail in the fall or winter when its pretty, fuzzy heads show up as they do at the right. The fuzzy things are the remains of flowering heads, or inflorescences. At the left you see a single foxtail inflorescence in the flowering stage, shown at about life size. Each of those hundreds of greenish, oval things making up the inflorescence is a flower or, more technically, a floret. The hairlike bristles sticking out all over the inflorescence are typical of foxtail grasses.
At the right you can see a close-up of a small section of inflorescence, and to understand what you're seeing you may need to review our Standard Blossom page. The brownish, frankfurter-shaped things on the left side of the picture are pollen-producing anthers held high on their slender filaments. The purplish, fuzzy items on the picture's right side are stigmas. To keep from self-pollinating, a flower's stamens mature first, then when the anthers fall away the stigmas emerge and begin collecting pollen from other flowers.
At the left you see a single flower topped with a fuzzy stigma. Grasses are wind-pollinated so it makes sense that the stigma is so fuzzy because the fuzziness increases the stigma's surface area so that it's more likely to catch pollen. Technically, the bristles arising below the floret are considered to be the involucre. Our Standard Blossom page defines the involucre as "one or more whorls of bracts located close beneath a flower or flower-cluster." These bristles, then, are much-modified bracts. And our page defines "bract" as "a much-reduced leaf, especially the small or scale-like leaves in a flower cluster, or associated with flowers." Since a foxtail's bristles are nothing like a much-reduced leaf or scale, obviously they are very modified.
At the right is a cluster of flowers, a couple of them issuing stamens. Here you have another view of how the bristles arise below the flowers. On the floret with the tallest stamens, the one pointing to the image's top, left corner, you can barely see that rising up about one-third of the floret's length there's a sort of blunt-tipped scale. That's the first glume.
And where does all this lead to? As in other flowers, the ovary matures into a fruit. In the case of foxtail grass, the fruits can be referred to as grains, and those are two much-magnified grains at the left.