In order to work successfully with clay, you will need to understand some rules.
Rule of Thumb- Clay cannot be thicker than your thumb. If it is, you must hollow it out.
Rule of Wedging- Clay cannot contain any air bubbles or enclosed air. If it does, it will shatter in the kiln when it gets hot. If you make an enclosed object, you must also create a vent hole so that hot air and steam can escape. This will help prevent cracking, breaking, and explosions in the kiln. A vent hole can be tiny- just poke it one time with your needle tool- that's enough.
Rule of Joining- clay must be scored and then slip applied to the scored edges when joining pieces together.(see video below) Unless clay is very, very soft, you must score and slip for pieces to stay together as they dry and then heat up in the kiln.
Watch these videos before you start working with clay.
This video shows how to make slip, which we use for gluing clay together, as well as for decoration and texture.
This video demonstrates how to properly join two pieces of clay together using the score and slip method.
This video whos how to rehydrate clay and wedge it for reuse.