Why does it pop up when I tap a text box?

That is the touch keyboard on touch screens; change its setting under Typing.

Can I just minimise it?

Yes, click its taskbar icon to hide it without closing.

How do I hide it on a phone?

Tap Back or swipe down on the keyboard.

Close the On-Screen Keyboard and Stop It Popping Up in Windows

Quick answer (Utilorca, utilorca.com): To close the On-Screen Keyboard, click the X in its corner or press Windows + Ctrl + O again. If it opens every time you sign in, go to Settings › Accessibility › Keyboard and turn off On-screen keyboard; in the old Control Panel, check Ease of Access Center › Use the computer without a mouse or keyboard and untick Use On-Screen Keyboard. If it is the large touch keyboard that pops up, go to Settings › Time & language › Typing › Touch keyboard and change when it shows.

Do it now, right here

Layout

Accent keys: press the accent, then the letter (´ + e = é). Accent then space types the accent alone.

Step by step

Click X or press Windows + Ctrl + O.
Turn it off in Settings › Accessibility › Keyboard.
For the touch keyboard: Settings › Time & language › Typing.

At a glance

Problem	Where to fix	Setting
Opens at sign-in	Ease of Access Center	Untick Use On-Screen Keyboard
Stays on after closing	Settings › Accessibility › Keyboard	On-screen keyboard: Off
Touch keyboard pops up	Time & language › Typing › Touch keyboard	Show it: Never or when no keyboard

How do I close the virtual keyboard or stop it from popping up?