If you're new to creating tabs with essyguitartab.com jump to the notes section where you can learn how to begin creating and editing notes.
Otherwise you can explore the menu items to the left to find the topic you're looking for.
The tab area (the main white page) is where you create your tab. At its simplest, creating a new tab just means entering fret numbers on the appropriate strings. The musical notation above is then automatically generated.
Once you have created a note you can add articulations (bends, slides, hammer-ons, etc) or otherwise modify the note.