We'd need more information to better help you. Here's the docs on how to use filter, but generally, this is your formula:
Filter(DataSource, ColumnToFilter = Filtercriteria)
What is your data source, what column are you filtering by, what data type is the column, what criteria are you filtering with, what control type is it, is it a variable, etc...
For example, if you're filtering on a text column and the user has selected an option from a dropdown, it could look like:
Filter(DataSource, ColumnToFilter = Dropdown.Selected.Value)
