SD cards are not for apps. They are for your music, photos, videos, and documents.
Most versions of android do not support moving apps to the SD card. Of the ones that do, the feature is being slowly removed.
For you apps that use lots of data space (camera, maps, GPS navigation, games), check the settings in the individual apps to see if they allow the data to be stored on the SD card.
Otherwise:
Which phone?
Which version of android?
Which carrier?