1. To blow up something (or blow something up) means to fill it with air a balloon, or a car or bicycle tyre.
Example: Can you blow these balloons up for the party, please?
2. Blow up also means to suddenly get very angry.
Example: I lost her bike and she blew up at me.
3. When something blows up (or when somebody blows something up) it explodes.
Examples: The plane blew up after the crash.