Canon EOS 750D Instruction Manual page 209

If the camera does not focus on the desired target subject with automatic
AF point selection, select a zone or switch the AF method to [FlexiZone
- Single] and refocus.
The number of AF points varies, depending on the [A3: Aspect ratio]
setting. At [3:2], [4:3], and [16:9], there are 49 AF points. At [1:1], 35 AF
points.
Focus on the subject.
3
Aim the AF point over the subject and
press the shutter button halfway.
When focus is achieved, the AF point
will turn green and the beeper will
sound.
If focus is not achieved, the area
frame will turn orange.
Take the picture.
4
Check the focus and exposure, then
press the shutter button completely to
take the picture (p.192).
Using AF to Focus (AF Method)
209