There are several std's out there, several of them are… clahmidia(not sure of the spelling), syphlis,gonorrhea and then there is also AIDS, not sure what any of the symptoms are as i've never had an std, contact your doctor or health department for testing for stds
Sometimes referred to as STI now, which stands for sexually transmissible infection. disease is the result of it kinda getting out of control i guess. there are many signs and symptoms, but some common ones are a rash around the genitals or mouth, perhaps lethargy.. may progress into more severe symptoms. Depends which STI you have. 
std are diseases in which you carry and contract to each other by sexual intercourse there are alot of them if you think you have one then you should consult your doctor quickly!!! many people are un aware that they have them but as soon as they have sex with someone they give it to them and it causes misery and alot of embarassment for either person….. look it up on google and just type in the full std it should tell you more there..
in short, they are diseases that are transmitted only by having sex(intercourse, oral, etc.). Symptoms may not show up from 1 to 10 years later. symptoms differentiate for each STD you acquire