I've been reading about Professions in the Hunter book, and I don't get it? what do these really do for them? are they the fundamental equivalents of a "Clan" (in vampire)? does it give any convey special abilities? Seems to maybe give some additional specialties?
They're pretty straightforward. (p.56)
All hunters have a Profession. In many cases, this is a specific job title (Soldier, Clergyman, Technician), while in others, it describes his primary activity or interest focus, regardless of whether this is an actual “job” or not (Socialite, Criminal, Vagrant). Check out the Professions detailed on pp. 74-93 and determine which best suits your character concept. Each Profession has two Asset Skills, which represent training or areas of expertise that are particularly pertinent to that Profession. After choosing a Profession for your character, look at the Asset Skills listed for that Profession and choose a free Skill Specialty in one of them. (This will bring your character’s total starting Skill Specialties as to four.)
So, an additional starting specialty and access to Merits like Professional Training and the like. They're meant to be a way of providing specialization and niches for Tier 1 characters who don't have access to superhuman powers or resources.
Professional Training gives you (at low ranks) free Contacts and more Specialties, reflecting someone who is "good at his/her job" more than simply high levels of skill might impart. It's an incentive to have characters with background and continuing lives.