Once you have created tags, you can then apply the tags in your regular admin views. For this example we will be using the 'Inventory > Parts' views.
First, check the boxes next to the parts you wish to tag (remember you can hold shift to select multiple rows). (Please note Parts are now found under 'Inventory' and NOT 'Warehouse')
Next, click the 'Tags' dropdown at the top of the page and select the tag you wish to apply to the selected rows:
Now you will see the tags applied to the parts. Note: You may have to add the 'Tags' field to your view.