You can't use the SD card to store apps--it wouldn't work well if you were running the app and then removed the SD card by mistake or on purpose. There should be plenty of space in your internal storage (whether it's 16 GB or 32 GB) to install a large number of apps.
To use your SD card for photos and videos, use the stock File Manager app or a 3rd party file manager like ES File Explorer to create folders like "My Photos" or "My Videos" on the microSD card. You could then transfer photos and videos to these folders using the File Manager (or by inserting the microSD card into your computer and copying files from there onto the card).
Although most phone cameras give you the choice to change the default location for saving photos and videos (internal storage vs microSD card), my Asus TF300's stock camera doesn't have that option, so I'm guessing the TF700 doesn't either. If you want a camera that can save to the SD card, try Camera ZOOM FX.