Move all your files - videos, music, pictures, documents, etc. to the card. (Use a file manager like
Total Commander - in landscape view you can put the card on the right side and look for stuff on the left side and just drag and drop, like on a PC.) You can create any folder structure you like - copy the DCIM, Movies, Music and Pictures folders completely, or make your own folders. Android doesn't care - it finds media wherever the files are. (In Gallery and Photos, the "album" names are the names of the folders the pictures are in.) You'll probably want to keep your music folder structure intact, because the folder setup is artist->album->track. Copy all your music to one folder and you lose that. (You can still play the track, but you can't find what you want as easily.)
Moving apps is possible - with some apps. (Some will move but not work - because the "developer" didn't know enough to check whether his app worked when moved, and if it didn't, to not let it be moved.) Open Application manager, choose an app and if the Move to SD button isn't grayed out, you can move the app. Then test it carefully and if there are any problems go back, the button will be labeled Move to Device, and move it back.
BTW, you don't have much internal storage "available" - Android needs a few hundred MB for itself. You can probably use about another 400MB before you start running into terrible lag.