I believe what you're looking for is the following:
tell application "System Events"
keystroke "?H" --(this will type '?' then 'H')
end tell
or for something like command-H:
tell application "System Events"
keystroke "H" using {command down} --(this will type command and 'H' at the same time)
end tell
finally, you can do something like the following:
tell application "System Events"
key down "?" -- press (and hold) '?' key down
key down "H" -- press (and hold) 'H' key down
delay 2
key up "?" --release '?' key
key up "H" -- release 'H' key
end tell