As with many cellphones, you probably can't.
Apps must be installed to the cellphone's internal storage, although a few apps like dictionaries will allow you to download the database to the memory card, in which case you'll see a clear prompt to accept that option.
The memory card is for camera pics, camera videos, downloaded MP3 tracks & videos.
Any of those which are currently in the phone's internal storage can be moved to the memory card to free up internal storage space.
It's should be fairly intuitive as to how to achieve that, or you should RTFM.
If camera always save pics & videos to internal storage, check the settings in the camera screen.