What Tab? Most don't allow apps to be installed on an SD Card because it can do more harm than good. SD Cards tend to be much slower than internal storage causing performance issues and if the SD Card fails it becomes a mess usually resulting in the tablet needing to be factory reset and if the tab dies the files on the SD Card become inaccessible.
If your tab does support it, the feature is likely called adoptable storage, without knowing what tab you have its unlikely anyone here can give you step by step directions for setting it up.
The SD card is best used for your photos, videos, music, and documents.
Leave the apps on the internal storage where they belong.
For the apps that use lots of storage space (camera, games, GPS, maps) check the settings of the individual apps. Many now let you pick the SD card as there data storage location while leaving the app on the internal storage.