Label Contract
Whether it has a somebody to tell me about contract and send demos to other labels.When you sign the contract with one label can you send demos to other labels and sign another contract.Hope you understand 
Unless the contract states so, you are not an exclusive artist to that label, meaning you can do whatever you want with the rest of your productions.
Yes. It all depends on the contract you sign. Now-a-days most people don’t get signed to a label, just one song or so. However, there are those that get signed to a label. At first, Skillex was signed to Deadmau5. Pretty sure Cazzette is signed to Avicii. It depends. Just make sure you and the label you have the contract with have the same understanding so you don’t do something that leads to a law suit.