To find issues that are assigned to, commented by, reported by, or starred for you, select a predefined search option from the Issues drop-down menu:
For all other searches, whether simple or very complex, enter a query. You can search for issues across the entire YouTrack server or in selected projects using a wide range of search criteria.
To get started, move the focus to the search box. If the focus is anywhere outside of the search box, just press Esc to move it back. Then, enter a search query.