hotkeys change for each race. u can see what hotkey does what by hovering over the icon with your mouse and the highlighted letter in the name of the unit/buildings/spell is the hotkey, plue F1, F2, and F3 correspond to your first, second and third heros. hitting F1 will select the first hero you built, and F3 the third. hitting alt should display a HP bar over all the units in the screen. Alt + G will create a minimap ping.
As for what to expect on Bnet... expect alot of assholes, and dont expect easy matchups. it will prolly take some time to win ur first match, cause alot of ppl make new accounts, and other abuse.