i3wm: how to configure touchpad?

The easiest way to do it is with synclient.

Use:

synclient -l

to list all options and their current settings and then you can use:

synclient var1=value1 [var2=value2] ...

to change the different options.

To make changes permanent you can either create a script and run it on i3 logon or edit the file /etc/X11/xorg.conf.d (if you don't have it copy it from /etc/X11/xorg.conf.d/50-synaptics.conf ). In /etc/X11/xorg.conf.d you should write your settings under:

Section "InputClass"
Identifier "touchpad"
Driver "synaptics"
MatchIsTouchpad "on"

In the form:

Option "var1" "value1"
...

For tap-click and vertical scroll on right you should add:

Option "TapButton1" "1"
Option "VertEdgeScroll" "0"

You can also take a look at arch linux wiki page about Touchpad_Synaptics

If you want more gestures take a look at touchegg

Since Touchpad Synaptics is no longer actively updated you can use libinput instead.

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

Section "InputClass"
    Identifier "touchpad"
    Driver "libinput"
    MatchIsTouchpad "on"
    Option "Tapping" "on"
    Option "ScrollMethod" "edge"
EndSection

Here are all options listed.