Inline editing can be extremely helpful for editing records without ever having to open them. We have a helpful article on using Inline Editing within List Views. But you may not be set up to use inline editing yet. Here's how to enable inline editing.
Navigate to Setup
Search for and click on "User Interface" in the left Setup pane.
Setup > App Setup > Customize > User Interface
Make sure that 'Inline Editing' and 'Enable Enhanced Lists' are checked, then click 'Save'. That's it!
Troubleshooting Inline Editing for a Specific Field
If Inline Editing is already enabled in your system but you are having trouble editing one specific field, you'll want to check the field accessibility to be sure that specific Field is Editable as well.
Navigate to Setup
Go to the Create > Objects menu
Choose the object where the field resides that you are unable to Inline Edit. In this example, I am having problems with the 'Confirmed On' date field on the Appointment, so I will go to the Appointment object.
Click on the Field Label of the field you are having problems with.
Click on View Field Accessibility
Select the field from the dropdown list:
Click on Hidden to change the visibility of the field.
Check the Visible checkbox next to the Page Layout, to ensure the field is visible in the page layout and click Save.
You can select the Field again from the dropdown list to ensure your changes have taken effect for all impacted User Profiles.
Once you have confirmed that the Field is visible in the Page Layout, return to the List View and attempt to Inline Edit again.