macbook air storage expansion

I have a Macbook Air 1.7 GHz,4GB 1333MHz DDR3 with a 256gb hard drive. Currently I have only 15 GB free.

I have purchased a 128gb jet drive storage expansion card on the recommendation of a tech at the Apple store.

I am looking to move my Photos onto it and have my phone photos back up there in the future so I can free up about 70GB of space. The tech in the store made it sound easy but I have not been able to figure it out. I am not very tech savvy. Thank you.