The search bar is a feature within the site that allows users to search for records and apps on the site. The search bar is a very beneficial tool because it can make navigating across the site much simpler and quicker. The app search bar is useful if a user is on a site that has many apps and is looking for a particular one, it would be more efficient to use the search bar than scroll and manually look for the app. The app search bar also provides accurate result depending on how specific the users search is.
The report search bar works similarly to the app level search bar. The report level search bar enables users to search through the list report they are on for the record they want. The more accurate your search is, the more specific the result. E.g. simply searching 'd' will return all records beginning with 'd' whereas searching 'demo' will return all reports that has 'demo' in its name. The search bar searches through records fields that have been specifically selected so that if you search for a record that has Demo in the title it won't search for records with Demo in the description unless selected.
The Global search bar is similar to the report search bar but instead of searching one specific report for the records you want (based filtered reports that could limit your search), it will search the whole app and create a app search report based off the layout of the default report and display it for you there. Please remember that this is a system provided report and will not stay there for the next time you come back to the app unless you use the global search bar again.