A filter specifies a set of rules for determine if a object matches the filter. A rule may be something like “the date is after 2025-01-01” or “the title contains the word wobbly”.
Filters may be either public or private; private means that only the user who created the filter can see/use the filter. A filter may be inverted, so that it returns the objects that do not match.
Filters may be marked as “use everywhere”; this makes the filter available whenever you can select a filter for the relevant object. The opposite means that the filter is only ever available from the page where it was created, f.ex. from the Search with filter page. This can prevent clutter if you have many filters.
Editing
You add rules to a filter by dragging a field from the right side list of fields to the pink box on the left side. There may be multiple pink boxes, these are called filter groups and contain a set of rules.
For each filter group you can select if all rules should apply in order for the filter group to be a match, or if just any one rules should apply. Similarly you can select if all filter groups should match for the filter to match, or if just any one filter group should match.
Next: 7. Update filters