i3 is a tiling window manager.It is not your typical desktop environment.

We are used to have a button somewhere we can click on to get a menu popup. In openbox we need to right mouse click the desktop.

In i3 we need to remember the following shortcuts to get to a menu.

SUPER + SHIFT + D is the dmenu
ALT + F3 is xfce application menu
ALT + F2 is gmrun
Super + F11 or F12 is rofi menu

Running applications can be done with your keyboard shortcuts.  So I suggest you read ~/.config/i3/config