A schema is a collection of database objects (as far as this hour is concerned—tables) associated with one particular database username. This username is called the schema owner, or the owner of the related group of objects. You may have one or multiple schemas in a database. The user is only associated with the schema of the same name and often the terms will be used interchangeably. Basically, any user who creates an object has just created it in her own schema unless she specifically instructs it to be created in another one. So, based on a user's privileges within the database, the user has control over objects that are created, manipulated, and deleted. A schema can consist of a single table and has no limits to the number of objects that it may contain, unless restricted by a specific database implementation.
Say you have been issued a database username and password by the database administrator. Your username is USER1. Suppose you log on to the database and then create a table called EMPLOYEE_TBL. According to the database, your table's actual name is USER1.EMPLOYEE_TBL. The schema name for that table is USER1, which is also the owner of that table. You have just created the first table of a schema.
The good thing about schemas is that when you access a table that you own (in your own schema), you do not have to refer to the schema name. For instance, you could refer to your table as either one of the following:
...
use[DB_name],
GO
IF SCHEMA_ID(N'dbo') is null execute(N'CREATE SCHEMA[dbo]');
GO