Ive never been to a bar

[DBowling]

im leaving to go to portland in an hour or so. i just turned 21 a few days ago. ive never been to a bar, but i plan to go while im there. do i pay per drink or can i open a tab anywhere? do all bars accept credit cards or should i plan on paying cash? and how does tipping work? Is my tip based on the number of drinks or the total bill? And finally, do i tip more for mixed drinks than i would a beer? Or is it all the same?
Thanks,
DB