What does a endocrinology doctor do? and why would i need a bath suit to go see that kind of doctor?

soo i am supposed 2 be tested for diabetes which i am and they said my insulin levels are high... i am 12. doles tht mean i have diabetes and if i am going to a endocrinology doctor why do i need a bathing suit... what do they do and should ni be scared because i am i am sitting here cryingg... plzz if u know plz help! thanks!