You can transfer files between a MacBook and an iMac in many ways, including over a wireless network, with an Ethernet cable or on a flash drive. The only way that doesn't require any additional devices, though, is Bluetooth. You need to set up both of the Macs to communicate using Bluetooth, but once you have, you can transfer files between them easily and quickly.
Click the Bluetooth icon in the menu bar at the top of the screen on both your iMac and your MacBook and select "Turn Bluetooth On."
Click the Bluetooth icon again and click the "Discoverable" option. Do this on both Macs.
Click the Bluetooth icon in the menu bar of your iMac and choose "Set Up Bluetooth Device."
Click on your MacBook in the list of Bluetooth enabled devices found by your iMac and click continue.
Verify that you are connecting to the correct device by clicking "Continue" in the dialogue box on both your MacBook and your iMac. Your MacBook will now be connected to your iMac via Bluetooth. You have to do this process only the first time you wish to connect the Macs, and the pairing will be remembered for future use.
Open Finder from your Mac OS X dock on either Mac and open the Applications folder. Open the Utilities folder and double-click the Bluetooth File Exchange icon.
Navigate to the file that you wish to transfer to your other Mac, and click "Send."