Developer Console in Salesforce

This Developer console is accessed by clicking on the setup (Gear Icon).

Once you click on Developer Console, then you can find a similar page as below:

This page use for the purpose as mentioned below:

1. Create Apex Class
2. Create Visualforce Page.
3. Create Lightning app
4. Create Lightning component
5. Create Lightning event & token and Interface
6. Open execute anonymous window
7. To see logs
8. To see code coverage
9. Query edition to run SOSL &  SOQL