CRUD stands for “Create, Read, Update, Delete”. Those are four base types of queries which you use when deal with a database.
When you work with table data, you think of it in terms of data rows. A table's record is a data row. Within a query you can operate on a single row either multiple rows. You can consider this as follows: a table is an array of objects which have the same type. A row is an object and a column is an object field.
Now, before starting to master your SQL skills, you should learn about four SQL statements which you use for CRUD functions.