To access a database in C#, you need to follow these general steps:

1- Install the required database driver or package, such as System.Data.SqlClient for SQL Server.

2- Create a connection string that contains information about the server name, database name, and authentication details.

3- Create a connection object using the connection string and open the connection.

4- Create a SQL command object and set its CommandText property to a valid SQL statement, such as a SELECT query or an INSERT statement.

5- (Optional) Add any parameters to the command object using its Parameters collection.

6- Execute the command by calling ExecuteNonQuery() for non-query statements or ExecuteReader() for SELECT queries. The result will be returned as a DataReader object.

7- (Optional) Process the result set by iterating over the DataReader object and reading its values using the GetXXX() methods, where XXX is the data type of the column being read.

8- Close the DataReader and the connection objects to release resources.

Here's some sample code to access a SQL Server database: 

Note that this is just a simple example and there are many variations of how to access a database depending on the specific requirements and database type.