Window managers determine where applications appear on your screen. Window managers handle tasks like: moving a window from one side of a screen to another, minimizing applications, choosing which application is in focus, showing your desktop, and more. Almost every computer has a window manager.
A tilling window manager forces all applications to exist on a grid (e.g. full screen, half screen, quarter screen...). Most of what you do is already on a grid: very few people use applications that are not in full or split screen. If your applications are not overlapping, you are in a grid format. By forcing windows onto a grid, you can vastly improve keybindings and, in turn, increase productivity.
Mod = Windows by default
Mod +Enter | open new terminal
Mod + Shift + q | close current window
Mod +0 ... Mod+9 | swap to workstation 0-9 respectively
Mod +Shift+ 0 ... Mod+Shift+9 | send current window to workstation 0-9 respectively
Mod + h | change focus one window to the left
Mod + j | change focus one window up
Mod + k | change focus one window down
Mod + l | change focus one window to the right
Mod + h+shift | swap cur window with one window to the left
Mod + j+shift | swap cur window with one window up
Mod + k+shift | swap cur window with one window down
Mod + l+shift | swap cur window with one window to the right
Just calling ./twm will not work. There can only be one window manager running at a time and you likely already have one going. You, in turn, have two options: use a virtual machine (recommended) or set this as your current window manager. (Note: this is for linux only)
I advise getting Xephyr: it allows you to run a second window manager in a toy display. Unlike normal virtual machines, Xephyr runs in the same environment: you still can access all of your files and interact with programs running on your machine. After getting Xephyr you should install xterm. You can then call ./run.sh to launch the Xephyr environment.
If you want to use this as your actual window manager I would advise looking into dex for Ubuntu / Arch. Essentially just bind ./twm to run on start up. Window managers are fairly integral pieces of software so, it is not a good idea to use one that you don't trust (e.g. mine).