An object that's cracked has broken and split into pieces.
You'll often hear someone say their phone screen or mirror is cracked after it fell on the floor. Sometimes people get a crack in their favorite mug when they drop it, but it doesn't break completely. A lot of times we use the word "cracked" to describe something that's been broken, like a record (a flat disc with music) or even just a feeling - if you're cracked under pressure, it means you're really stressed out.
Broken so that cracks appear on, or under, the surface.
