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).
Generally speaking, sexual misconduct means any sexual conduct that involves violence or lying. 

One kind of sex is no worse than the other. It all leads to suffering. 

I have never heard of anything on circumcision in the Buddha's teaching but there is a rule that monastics can't cut the penis clear off.