The functions that was of the Storage sensor in Windows Phone 8.1 are now (at least for the time being) in an app called Storage (IT: Memoria). From that app you can set to have new app, pictures, video to be stored in the SD: from then on new pictures and music will be stored on microSD, automatically.
If you want to move on microSD an app installed in the device you can do (even though now this must be done for every app one by one and it is not possible to select more and move all the selected!!) … but, for the time being, there is not a way, from that app, to move pictures and music you have on the device to the microSD. Therefore to transfer your existing files from the phone memory to the microSD, I am not aware of any other solution than using a File Manager app within your phone (e.g. I use File Explorer app) or using the File Manager of your PC once the smartphone is connected via USB.
Anyway I hope that there should be introduced an easier way inside that Storage app … and moreover in my opinion the storage functionalities should be included in Settings as it was in Windows 8.1!