Professional. What does the word professional means?

According to Oxford American Dictionaries:

pro•fes•sion•al |prəˈfe sh ənl|

adjective
of a person) engaged in a specified activity as one’s main paid occupation rather than as a pastime : a professional boxer.• having or showing the skill appropriate to a professional person; competent or skillful : their music is both memorable and professional.• worthy of or appropriate to a professional person : his professional expertise.

noun
a person engaged or qualified in a profession : professionals such as lawyers and surveyors.• a person engaged in a specified activity, esp. a sport or branch of the performing arts, as a main paid occupation rather than as a pastime.• a person competent or skilled in a particular activity : she was a real professional on stage.

That I gather a professional is a person gets paid for the work they do, as to a hobby.

What is hobby?

hob•by |ˈhäbē|

noun ( pl. -bies)
an activity done regularly in one’s leisure time for pleasure : her hobbies are reading and gardening.2 archaic a small horse or pony.• historical an early type of velocipede.

So my question is how does one turn a hobby (an activity do not get paid for) into a professional (an activity one gets paid for)?