Can anyone please tell me what's happening in this code? I'm stuck here for like past 3-4 days

This is a code snippet I from the code I was given by a friend. I'd appreciate if someone could explain as to what is happening in there in detail. Thanks.

  module.exports.loadDb = function (dbFile, cb) {
      fs.readFile(dbFile, function (err, res) {
        if (err) { return cb(err) }

        var messages
        try {
      messages = JSON.parse(res)
    } catch (e) {
      return cb(err)
    }

    return cb(null, { file: dbFile, messages: messages })
  })
}

This function is being used to get to the inbox stored in a JSON file but what exactly is going on in there??

module.exports.findInbox = function (db, encodedName) {
  var messages = db.messages
  return {
    dir: path.dirname(db.file),
    messages: Object.keys(messages).reduce(function (acc, key) {
      if (messages[key].to === encodedName) {
        return acc.concat({
          hash: key,
          lastHash: messages[key].last,
          from: messages[key].from
        })
          } else { return acc }
        }, [])
     }
    }


module.exports.findNextMessage = function (inbox, lastHash) {
  // find the message which comes after lastHash
  var found
  for (var i = 0; i < inbox.messages.length; i += 1) {
    if (inbox.messages[i].lastHash === lastHash) {
      found = i
      break
    }
  }

  // read and decode the message
  return 'from: ' + decode(inbox.messages[found].from) + '\n---\n' +
    decode(fs.readFile(path.join(inbox.dir, inbox.messages[found].hash), 'utf8'))
}

via Farhat Nawaz