When using burned, it applies that (Someone) or (Something) has done the action of "Burning".
When using burnt, it simply means that (Something) or (Someone) is burnt
To simplify,
He burned his arm
or
We burned the planks to start a fire
The sentences consist of a Subject, Object and Verb.
But to use burnt, it would only need a Subject and Verb
For example
The toast is burnt
My skin is burnt from the sun
If you still are confused, I can explain more briefly.
This can also be applied to learned or learnt, and any verb similar.
Though Learnt and Burnt don't register to the English language, it's moreover a slang word.