What OS are you running? Lollipop does not allow apps to be moved to an external card. I believe Marshmallow does.
I am on lollipop and apps can be moved to SD.
There is no default way so that new apps automatically go to SD. Only with photos and videos you take with the camera can you do that.
As far as apps, when you install new ones, you have to individually move then to SD.
Go to application manager in settings, go to the app and click "move to SD". Be aware of a couple of things. On large apps such as games, not everything moves to SD, some of it remains on internal storage. And when you update the app, it gets moved back to internal storage and you have to move it back again to SD. This is a pain, trust me.
If you do this, 3rd party app movers are better. I suggest AppMgr III. It tells you detailed information about which apps can be moved to SD, and what functions are lost if you do. Something you won't know if you move it yourself via application manager. Some apps retain all functionality when you move to SD, some can't be moved and many apps can but lose features such as widgets. AppMgr III tells you exactly.
With my experiences, I suggest keeping the SD for photos, videos and music only.