Quote:
To be honest I don't really know the chords.. because I never learned that much about chords xD
My keyboard says, E B Cm A.
Yup transposed to a different key.

You are playing in the key of E it can be played with a different key by changing the chords/notes as they are arranged. Same thing as placing the "Capo" on your guitar frets.
(LOW) E F F# G G# A A# B C C# D then back to E on the 12th fret.
A A# B C C# D E F F# G G# then back to A on the 12th fret.
D E F F# G G# A A# B C C# then back to D on the 12th fret.
G G# A A# B C C# D E F F# then back to G on the 12th fret.
B C C# D E F F# G G# A A# then back to B on the 12th fret.
(HIGH) E F F# G G# A A# B C C# D then back to E on the 12th fret.
Place a capo on the first fret and you are playing in the key of F.

You can transpose on Piano by the arrangement of these notes.
If you have a progression of G D E minor C
You can arrange to the key of E by notes like this
G would be E (D E F G) - between the E and G is one note so...
G becomes E
D becomes B
E/minor becomes C/minor
C becomes A
See how easy it is to change keys?

You could also play the arrangement in a key that fits your tonal voicing.That is what keys are for.
You could play it as
G D E/minor C to
Key of F (F G - one note difference) - F C D/minor B
Key of D ( D E F G two note difference) - D A B/minor G
The first chord/note usually determines the key.