Cassandra Query Language (CQL) is the default and primary interface into the Cassandra DBMS. Using CQL is similar to using SQL (Structured Query Language). The concept of a table having rows and columns is almost the same in CQL and SQL. The main difference is that Cassandra does not support joins or subqueries, except for batch analysis through Hive. Instead, Cassandra emphasizes denormalization through CQL features like collections and clustering specified at the schema level.
CQL is the recommended way to interact with Cassandra. The simplicity of reading and using CQL is an advantage over older Cassandra APIs.
The CQL documentation contains a data modeling section, examples, and reference information for each CQL command.