There are not many situations where you may need to substitute the mouse with the keyboard. Maybe your mouse just broke down and you need to finish a job before you can get a new one, or your notebook's touchpad is broken and you do not have a mouse in reach, or the battery of your wireless mouse just did and needs to recharge.
Whatever the reason, if you require a mouse but do not have one, you can use the keyboard instead.
The Windows operating system comes with options to use the keyboard for that, but it is not enabled by default. You can enable it temporarily with the keyboard shortcut To do so, type "ease of access" on the search or run box of your system and select the result that opens up.
The "Make the mouse easier to use" menu is what you want to open. Here you need to enable the "turn on mouse keys" feature. Basically, it enables you to use the numpad keys as a mouse substitute.
Once enabled, use the 1-4 and 6-9 keys to move the mouse pointer in the selected direction, the key 5 to right click and left click.