HIV is found in blood, cum (semen), vaginal fluids and breast milk.
 
The most common ways of transmitting HIV are through unprotected (condomless) sexual intercourse (oral, vaginal and anal sex), sharing injecting equipment and to a child during birth or pregnancy.
The vrius can only be passedto someone else if the person living with HIV has a 'detectable' viral load  - meaning that the levels of the HIV in the persons blood are high enough to cause onward transmission.
Someone living with diagnosed HIV and taking effective medication can reach a point where the virus is 'undetectable' in the blood. This means the levels of HIV are so low they cannot pass the virus on to HIV negative people.