To allow your users to add items, head to the
Add section in the right sidebar and enable the checkbox 'Allow users to add items'.
A plus sign will now appear in the top right of your list views. When you click this your add screen will show up and your users will be able to add items to your app.
If you don't see newly added items in your sheet, scroll all the way to the bottom to check if they are being added after empty rows. By default, new Google Sheets contain 1,000 empty rows, but for a variety of reasons, these rows can appear non-empty to Glide.
After the plus sign is clicked, a new set of components is shown on the right panel. These are your
Add Components. Glide will automatically generate these for you based on the columns in your sheet. You can remove components for columns you don't want users to be able to add to and you can change the type of components that users use to enter data.