The Search function is a full-text search that allows you to search across the system to find any existing field or record. So you are searching for a person by name, phone, email or business; or possibly an invoice (and its number), the search will produce results relating to your search criteria. Simply enter your criteria in the search line and click on the magnifying glass (or tap Enter) to submit your search and load the page with the results.
When your results are loaded, you may then filter your results by Type (Entity containing your search criteria).