Unlike transabdominal pelvic ultrasound where the transducer is placed on the skin, transvaginal pelvic ultrasound is an internal examination where the probe is placed into the vagina. This produces more detailed images of the gynecologic structures, such as endometrium within uterus as well lesions or cysts within the ovaries.
It is a hard but very smooth plastic wand with a bulbous end, which is inserted first, well-lubricated. The bulb is pressed against the walls of your vagina, and then the "sound waves" go forth, which can be an odd sensation but not really painful. I don't recall any particular audible sounds, however.
You can watch on the monitor, and most of my techs enjoyed explaining what you are seeing.
Usually pain free unless you get a sadistic tech performing your evaluation. (Definitely better than a metal speculum, however. lol)
Older women may wish to have the tech assist them afterward in getting their feet out of the stirrups, and standing up from the table...unless you get a sadistic tech...just saying...