First I would suggest clearing out your cache, history, etc., of apps like your browser, Facebook, Messaging, etc. Any app that keeps large amounts of history and data on the device. Just be sure you save anything you want or need before doing so.
Now if you want to just move files to free up space (photos, videos, music, etc.), not apps, to the SD card you can use the file manager app that is on the device, or if there isn't one you can download and install one to access and move the files. Sadly, they usually only let you move one or two at a time.
To move them all at once, or in large amounts, you can connect the phone to a computer via USB cord, then move the files over to an empty folder on the computer. Once there, and still...