Installing My Passport For Mac On El Capitan

Hi, I purchased My Passport for Mac to replace an old My Book on my iMac with El Capitan. I want to find out if it will be easy for me to install it on my iMac and also be able to transfer my back up from My Book easily to My Passport. If I can transfer my back up how do I do it?. I am not a computer techie. Thank You for your help.

Hello, what software did you use to do the backup?

Thank you for answering my question. The back up that is on my old My Book was used with Snow Leopard and also now it has El Capitan on it. I am concerned that first of all the My Passport for Mac that I purchased will not work with the El Capitan and that I will lose all of the back up on my old My Book if I install this new My Passport for Mac I have not installed My Passport for Mac yet as I am not sure if I should return it. I need some back up for my new iMac as my old My Book stopped working but with help I got it going again. I was told that it is too old. Thank you for any help that you can give to me.