Where can I find the missing start button?

[junosa]

Where can the start button be found on the HP computer Windows 10. On the left on the bottom task bar is a square with a plus sign in it.

[Prométhée]

Hello
it's a window ... windows logo
This changes depending on the version (1809 1903 ..)
it may be different for you
to make it clear!

in image (but it may be different for you)

click on it with the left button:

with right

[WAWood]

@junosa 

As @Prométhée indicated, there is no longer a START button -- as MS got rid of that, and the entire Start Menu, with Windows 8 -- because they were convinced, like their INTERNAL folks at Redmond, that EVERYONE was abandoning Desktops and moving exclusively to Tablets -- so they need what was, essentially, a "smartphone-like" interface with big buttons and NO menus.

Fast forward to Win 10, and in the interim, Stardock made MILLIONS of dollars selling their replacement for the Start Menu, known as Start 8, and upgraded that a few years ago to Start 10.

MS NOW have a button there, but if you don't like that, there are replacements you can download and install:    https://silicophilic.com/windows-10-start-menu-replacements/

My favorite is Start 10 from Stardock (largely because I was an early adopter and fan of Start 8), but others work equally well.

[Prométhée]

yes, too, but no need to install anything
We can just use a shortcut, or even a
key combination!
(alt and f4)

https://www.digitalcitizen.life/7-ways-shut-down-or-restart-windows-10-pc-or-device

https://www.isunshare.com/windows-10/create-a-shutdown-shortcut-on-windows-10-desktop.html