To add data into a database after its creation, the SQL command 'INSERT' is used. This command allows you to insert data into specific columns of a table in the database. The syntax of the INSERT command specifies the table to insert into, the columns to populate, and the values to enter into those columns. This is fundamental in database management and manipulation, critical for developers working with databases.References: INSERT is a basic and essential SQL command covered under database operations in CompTIA IT Fundamentals and other foundational IT curricula focusing on software development and database management.