Canon EOS 7D Instruction Manual page 148

Using AF to Focus
You cannot take a picture during autofocusing. Take the picture only while
the Live View image is displayed.
148
3
Focus the subject.
Aim the AF points over the subjects

and press the shutter button halfway.

The Live View image will turn off, the
reflex mirror will go back down, and
AF will be executed.
 When focus is achieved, the beeper
will sound and the Live View image
will reappear.
 The AF point used to focus will be
displayed in red.
4
Take the picture.
Check the focus and exposure, then

press the shutter button completely to
take the picture (p.136).