If you just installed i3 on a laptop and for some reason you can’t tap or the scrolling behavior doesn’t like you, you can update how the touchpad behaves using a xorg config file.

In my case the scrolling behaviour wasn’t the one I like, so I modified the NaturalScrolling property.

## /etc/X11/xorg.conf.d/30-touchpad.conf

Section "InputClass"
    Identifier "touchpad"
    Driver "libinput"
    MatchIsTouchpad "on"
    Option "Tapping" "on"
    Option "NaturalScrolling" "true"

You can see all the available options.

More info about libinput