this is my first time
I bid $37.50 on an item with a current bid of $11.76
and one day, six hours left

will my bid of 37.50 automatically be bid
OR will only the amount necessary to win the item be bid
(eg: $11.77)

thanks

Your bid of 37.50 will be done, but you will win it for 12.26 (11.76 + 0.50 increment), considering there are no other bidders.
If there are other bidders, you will not pay above 37.50.