Hepatitis A is transmitted when traces of faeces enter the mouth, either via unclean food and water (in southern countries) or during sex. The pathogens which cause hepatitis B are primarily present in the blood, but also in other bodily fluids such as semen and saliva. Hepatitis B is usually transmitted during sex.
The virus which causes hepatitis C is present in the blood. It is often passed on by sharing needles when injecting drugs. More rarely, it can also be passed on when snorting drugs such as cocaine, if multiple people use the same tube to inhale. Transmission during sex is very rare, but it can occur - primarily in men who have sex with men.