Star formation begins in the molecular cloud where each dense core is initially in a balance between self-gravity, which tends to compress the object, and both gas pressure and magnetic pressure, which tend to inflate it.
Since the mass of the Milky Way galaxy is about 1011 M⊙ and its age is about 1010 years, we can calculate that at present, new stars are forming in the molecular cloud of the Milky Way at a rate of about three M⊙ per year.