GNOME 3 is a great desktop environment for everyone. For those like window snapping or tiling, probably the default behavior (side-by-side) of GNOME Shell is not satisfying. Fortunately, there are two extension to do window snapping/tiling more in GNOME. You may do tiling for more than 2 windows with them. For example, tiling 3 windows or 4 windows side by side. Here we show them with their installation links.
GNOME gives you default behaviour to do window snapping (or window tiling). By pressing Win+Arrow Key your current window will be tiled automatically. Defualt snapping windows for GNOME Shell 3.18.1 allows only half-display snapping. It means you can only tile two different windows side by side. You can't have four different windows tiling in four desktop corners.
Picture below showing Writer and Firefox windows tiled side by side.
Fortunately, there is an extension if you love to tile your windows in GNOME Shell desktop. It is ShellShape by gfxmonk. ShellShape gives you a button in your top panel, and you can change your windows tiling mode by selecting one preset available. In picture below, ShellShape tiles three windows in vertical mode.
Download Extension: https://extensions.gnome.org/extension/294/shellshape/
More fortunately, there is another good extension. It is Gtile by vibou_. Gtile works with its own tiles map representing your display screen length x height. Gtile allows you to tile your active windows, four windows for four corners (4x4). If you have larger display, then you may choose to tile 6x4 or even 8x4. To use it, click its button in the top panel > click one tile > click another tile to make square selection > your active window will be tiled according to your selection. You may choose to do tiling manually for one window or automatically for all window simultaneously.
Download extension: https://extensions.gnome.org/extension/28/gtile/