Most deck designs are based on a number of posts that rest on concrete footings or are imbedded in concrete and in turn these posts take the weight of the deck.
Each structural member of the deck is designed to take weight and transfer it through connection to the ground. The decking material, takes the weight of the people and items that are on the deck, this weight is transferred to floor joists, which in turn transfer the load to the beams which in turn transfer the load to the posts which take the load to the ground.
Although the aforementioned construction method provides the best possible support, there are some variations that can be utilized. You can notch the post so that only one of the beam members is actually resting on the post and the other is bolted to the first beam. Adding a support that is well fastened to the beam increases the strength.
The same construction scenario applies to the floor joists that connect to the beams. It is best if the floor joists sit on top of the beams, however in some cases this is not possible due to height problems from the ground to the base of the deck. In those cases there are brackets, called joist hangers, which are designed to make the connection and transfer the load. Joist hangers come in a variety of sizes that will suit any size floor joist in combinations of one, two, or three joists tied together.