Question: What is it? Is sex just for pleasure with your partner breaking a precept? Eg with a condom. And is being circumcised bad over personal preferences/ (hygiene,aesthetic)? is oral and anal sex bad? Is masturbation bad? And is circumcising your sons bad?

Answer: 
Sexual misconduct is defined in the Pali scriptures as having sex with someone else's partner or fiancee and with those living under the protection of their parents or an institution (in the case parents, if the parents disapprove). 

The purpose of refraining from sexual misconduct is to not harm/damage existing relationships. 

Therefore, having sex for pleasure, using a condom, circumcision, masturbation & oral & anal sex are not, in themselves, sexual misconduct (even though some of these things can be unwholesome & unskilful).
In general, the Pali Canon is quite exoteric and seems to equate sexual misconduct with various kinds of adulteries. Of course, for a monastic any sexual activity at all with the sole exception of involuntary nocturnal emissions is forbidden by the Vinaya.