I.had a boil under my armpitt ..and it went down and its hard .underneath my skin like a small little bump .do boils, do that ?

Yes: Boils can take a long time to heal completely. The bump could also be a swollen lymph node as a result of the boil.

Granulation Tissue: Granulation tissue is composed of tissue matrix supporting a variety of cell types, most of which can be associated with one of the following functions: formation of extracellular matrix, operation of the immune system, or vascularisation. An excess of granulation tissue (caro luxurians) is informally referred to as "proud flesh.".

Yes :it's =carbuncle: A superficial skin abscess or boil can develop deeper tracts into the skin which can form a carbuncle or a deeper version of a boil.