Q: how do i left click on my macbook air?

Press down on the Trackpad to click.

If you go to the Trackpad System Preferences, you can enable tap to click, so you don't have to physically depress the Trackpad.

You can also turn on secondary click as two-finger tap.

Hi Mrs Wrght,

Control + Trackpad click (however you decide to set it for right-click as Barney has described above), is how you left-click something with a trackpad.

Cheers,

GB