Another important topic to know is Genital Ulcers.

In the USA, commonest STD with genital ulcers are Herpes (Painful), Syphilis (Painless) and Chancroid (Painful) (HSC).
In other countries, Gramuloma Inguinale (Donovanosis) & rarely Lymphogranuloma venereum (LGV) may be causes of a genital ulcer.

Specific tests include

Syphilis: Serology, and either darkfield examination or direct immunofluorescence test for T. pallidum;
HSV: Culture or antigen test for herpes simplex virus (HSV) &
Chancroid: Culture for H. ducreyi.
Biopsy of ulcer if indicated or if above tests are non diagnostic.

Inspite of complete diagnostic evaluation,  25% of patients with genital ulcers have no laboratory-confirmed diagnosis.

Chancroid (H. ducreyi) is treated with one of the following regimes.

Azithromycin 1 g orally in a single dose,
OR
Ceftriaxone 250 mg intramuscularly (IM) in a single dose,
OR
Ciprofloxacin 500 mg orally twice a day for 3 days, (Not for pregnant/breast feeding/less than 17 yrs age)
OR
Erythromycin base 500 mg orally three times a day for 7 days.

For treatment of herpes, review this link

Prevention of transmission of disease by either abstinence or by using condoms.