My iTunes files are on an external hard drive. how to access them

I have a new iMac with an SSD and a 1TB second drive. I backup the iMac 2nd hard drive to an portable external drive so I can carry my entire iMac file storage on an extended trip...5 months. What is the easy way of connecting my MBP iTunes app to the iTunes on the portable exernal hard drive so I can access stored movies, music etc.

Thanks

Steve