ETL is the process of extracting data from various sources, transforming it to fit operational needs, and loading it into a data warehouse or database. It involves extracting data from sources like DVDs, books, and friends, transforming it by cleaning and consolidating the data, and loading it into a data warehouse for storage and analysis. Migrating a database transfers data from one platform or format to another, such as moving from a Foxpro database to SQL Server. Data is inserted into databases using an INSERT statement specifying the table and values, with the values' data types matching the table's fields. Updates are made using an UPDATE statement to modify an existing record where a condition is met.