A chord consists of multiple notes played together that sound as one. On a stringed instrument this means holding down a series of notes and either playing them simultaneously by strumming, or plucking them one at a time in sequence.
Tabs stands for tablature and is a means of marking music by indicating at what fret, or point, the string should be held down. Tabs are designed for people who can't read standard music notation.
A tab is usually shown as several lines, each representing a different string, with a number on those lines at different points. The tab is read from left to right, playing notes by holding down each string in turn at the point the number indicates. A tab may also show the lyrics of a song with a chord over certain words indicating chord changes. Tabs are not able to indicate time signatures and rhythm so the player usually needs to be familiar with the song being played.