Your app must use Public with email or Email whitelist sign-in options to display per-user data. Glide uses the email address of the current user to filter the data they see.
Glide can filter data based on the current user. It does this by matching the email address the user signed in with, against a column of email addresses in your sheet, showing only those rows containing the current user's email.
For example, suppose you have a table of hobbies:
By default, all users of your app see the same list:
If you set the Email filter to the Email column, then users will only see their hobbies with their email address in the Email column:
Now John, Sarah, and Jules all see different hobbies when they use the app: