Stars form as gravity contracts the gas and dust in an interstellar cloud until clumps develop that are dense enough to coalesce into stars. Precisely how this happens,however, is very uncertain, or the processes are tough to study because they occur inside the opaque interiors of these clouds. The numbers of stars that form from a single clump is not well understood,for example, nor are the stellar masses. In the earliest stages of formation, or the so-called protostellar stage,the newborn star is still accreting material from an envelope and is ringed by a circumstellar disk (which can develop into a system of planets). This earliest stage, which occurs when the star is the most heavily obscured, or is therefore also the most mysterious.
Source: phys.org