Each horizontal line in guitar tabs represents a string of the guitar, with the bottom line being the thickest (low E) string and the top line being the thinnest (high E) string. The numbers on the lines indicate which fret to press on that string. For example, a "3" on the fifth line means to press the third fret on the A string.
Tabs can also include additional symbols and notation to indicate techniques such as hammer-ons, pull-offs, bends, slides, and vibrato. These symbols are usually written above or below the tab numbers.
Guitar tabs are often used by beginners as they provide a relatively easy way to learn how to play songs without having to read standard music notation. However, it's important to note that tabs only give you the basic information about what to play, not how to play it. To develop good technique and musicality, it is recommended to supplement your tab reading with lessons from a qualified guitar teacher or by studying other resources such as books, DVDs, and online tutorials.