What is a picklist?
Picklist is a drop down list with a predefined set of items. For the cells with picklist, one cannot manually enter any data to it. To populate the cells with picklist, one can only pick a value from the drop down list.
How to create a picklist?
Select the cell/cell range in which you wish to insert the picklist.
Navigate to Insert > Picklist > Create Picklist. Alternatively, you can select from the predefined list of picklists.
From the side pane that appears, you can either select Single-Select or Multi-Select.
Select how you wish to display the values—List or Cell Range.
Enable Display as chip if you wish to display the values as chips/bubbles inside the cell.
Select the preferred colors for the values in the picklist with color options drop-down.
Once you're done, click Create.

Editing a value from the picklist will effectively change the old value to the new one, in every occurrence until then. This saves you time and effort, and you'll not have to change it manually in every othere place!
How to use a picklist in another range?
If you have a picklist created for a range, and you want to use the same in another range as well, you can copy the picklist and use it else where, in the same work book. To use a picklist in another range: