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: 
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.
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.