You have to ask to get in. You don't know what you're getting into until it's too late.
I agree that you usually have to ask to join, although it is common for masons to suggest that members of their family join (as my grandfather did).
However there is both an interview and a vote on any new candidate.
As for what exactly it is you are getting into - I've spoken to a few masons (both in my family and outside) who have told me that in the 'average'
lodge, masonry is seen as nothing more sinister than the women's institute - just a group of men meeting to perform some rituals they don't
understand, make donations to charity and socialise.
I don't doubt that as with any organisation certain branches may well have other agendas, but I feel strongly that these elements use the masonic
organisation to shield themselves and perpetrate rumour, rather than representing freemasonry as a whole