There are two types of Suspended triads, a Sus2 and a Sus4 chord.  

 

Think of a  Sus2 chord as a Minor Triad in which the 3rd interval (ga) has been stepped down to a major 2nd interval (Re). 

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So, a Csus2 chord has the notes C, D, G instead of C, Eb, G (Sa, Re, Pa).

 

Similarly, a Sus4 chord is like a Major Triad in which the 3rd interval (Ga) has been stepped up to a  perfect fourth interval (ma). So, a Csus4 chord has the notes C, F, G instead of C, E, G (Sa, Re, ma).

 

Suspended chords create some sweet tension, give you the feeling of being suspended. So, when you hear a suspended chord, you feel like wanting it to resolve to a major or minor chord.  Try strumming Csus2 for a while and then C, and you will feel the sweet tension going away!

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Another interesting thing about suspended chords is that a Sus2 chord when inverted to start from its last note will become a Sus2 chord based on that note. So, if you take the notes of Csus2 chord (C, D, G) and invert it to start from the note, it will become a Gsus4 chord (G, C, D).