Teak is right but with a very short answer... In order for infection to occur, three things must happen:
1) You must be exposed to pre-***, semen, vaginal secretions, blood or breast milk,
AND
2) The virus must get directly into your bloodstream through some fresh cut, open sore, abrasion etc.,
AND
3) Transmission must occur, directly from one person to the other, very quickly (the virus does not survive more than a few minutes outside the body).