Sus2 stands for “suspended 2nd”. The 3rd of a minor or major chord is suspended and replaced by a major 2nd.
Comparison of sus2, minor, major and sus4: Csus2 has the tones: C (1), D (2) und G (5). Cm has the tones: C (1), Eb (m3) and G (5), C has the tones: C (1), E (3) and G (5), Csus4 has the tones: C (1), F (4) and G (5).
The Csus2 chord can be deduced from a C major or Cadd9 chord. On the piano that should be no problem at all, but on the guitar the voicing you get may be hardly playable. In that case, it needs more reconstruction. Ok, you need a major 2nd, get rid of all 3rds and end up with a playable chord!
Let's get the major 2nd (2) D:
• slide two frets down to D from the major 3rd E, or
• slide two frets up to D from an additional root C on one of the higher strings, or
• start with a Cadd9 chord: you already have the D. It's the 9 that becomes the 2 after you get rid of all major 3rds.
Tones that exist more than once:
• you can move up a dublicate 3rd to the 5th G by three frets (no problem, if the 5th exists two times).
• you can also just omit duplicate 3rds, 5ths or roots.
Where to play a sus2 chord: Usually a Csus2 chord is played instead of a plain C major chord. But since there is no 3rd and no 4th, it can be used nearly as unrestricted as a power chord (C5).
Everybody knows the sound of the chord progression Csus2 CCsus4 C or the other way round: Csus4 CCsus2 C.
The best way to play this is by starting off with chord shapes that are based on the basic A or D chords.
Attention: you can nearly always change a sus4 into a sus2 chord, but don't just do it the other way round. The sus2 chord on your lead sheet may just be meant as an add9 chord without the 3rd being played. In that case letting ring a 4th is like stumbling into a wasp's nest. So carefully ask your ears first!