what is the "Bearer <token>"

INSTRUCTION.pdf
API Documentation
there is input 'api_key' at top right corner. Paste there token in format: 'Bearer ' and click 'Explore'
i login get like this and i don't know what to do next,specialy 'Bearer '
{
"token": {
"expires_in": 3600000,
"access_token": "aaa.bbb.ccc",
"refresh_token": "ddd.eee.fff"
}
}