Here's some steps to ease you in:
Let's say we want to create a spinner button
to increase / decrease the value in say, cell A2
Steps
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Click View > Toolbars > Forms
Click on "Spinner" icon in the toolbar ("up/down arrow")
Hold down Alt key and draw the spinner
to fit over say B2:B3
(it will snap to the grid if you hold down Alt)
Right-click on the spinner > Format Control > Control tab
(Accept the default Incremental change, which is "1")
Put inside Cell link: $A$2 > OK
Now click on the up arrow of the spinner
Each click will increment the value in A2 by 1
Tinker around the spinner control - it's quite intuitive..