You can write a song, using chords from various keys,and you can get them to sound good, but generally there are a few simple rules to follow.

In any given key, certain chords are much better at following the previous chord than others.

Here is a chord leading reference guide.

The I chord can lead to any chord

The ii chord leads to to IV,V,vii

The iii chord leads to the ii,IV,vi

The IV chord leads to the I,iii,V,vii

The V chord leads to the I

The vi chord leads to the ii,IV,V,I

The vii chord leads to the I,iii

As a guide

I  ii  iii  IV V vi vii

C D  E   F  G A  B

So C   F   G Are Major chords

The  D  E  and A are minor chords

and B is diminished( not often used)

All chords can be altered to "colour chords" ie  Cadd9, Am7 etc.

Hope this helps, you get started at having a go at creating your own music.

K.Amess