If you want to have two apps open side-by-side, there is a very quick way to get Windows to do it for you to save you having to resize each one bit by bit. Drag the first app/window into the left side of the screen, release the mouse and Windows 10 will automatically resize that app/window to fill up your left half of your screen. Repeat the same thing for another app (or choose from the displayed list which other app you might want to fill up the right side of your screen).
Drag into the left of the screen…
Windows 10 will make it fill the left half of the screen…
If you have anything else open, Windows 10 will let you choose which app/window you want to fill up the right half of the screen…
Hey presto, two apps open side-by-side…