For instance, you are playing an A major chord.
fret note steps from root
E |---0----------e-----(5)------------------|
B |---2----------c#----(3)------------------|
G |---2----------a-----(r)------------------|
D |---2----------e-----(5)------------------|
A |---0----------a-----(r)------------------|
E |-----------------------------------------|
If you want to play an AMajSus2, you need to add a B. I usually sub for the C#, like this:
fret note steps from root
E |---0----------e-----(5)------------------|
B |---0----------b-----(2)------------------|
G |---2----------a-----(r)------------------|
D |---2----------e-----(5)------------------|
A |---0----------a-----(r)------------------|
E |-----------------------------------------|
Sometimes a 2 is called add9 (the root is the same as the 8 note, so the 2 note is the same as the 9 note).
This is one of many chords with a 2, and I am not sure it is the official sus2 chord. Someone with better theory knowledge will probably come along with a more complete answer. Until then, this will get you started with the idea.
