Export
Open VirtualBox and enter into the File option to choice Export Appliance...
You will then get an assistance window to help you generate the image.
1. Select the VM to export
2. Enter the output file path and name
1. You can choice a format, which I always leave the default OVF 1.
2. Finally you can write metadata like Version and Description
Now you have an OVA file that you can carry to whatever machine to use it.
Import
Open VirtualBox and enter into the File option to choice Import
You will then get an assistance window to help you loading the image.
1. Enter the path to the file that you have previously exported
Then you can modify the settings of the VM like RAM size, CPU, etc.
1. Press Import and done!
Now you have cloned the VM from the host machine into another one