# User-defined functions in ksqlDB for Confluent Platform User-defined functions (UDFs) let you add new functions to ksqlDB using Java hooks, extending the broad range of built-in functions it ships with. Learn how to use them in the [how-to guide](../how-to-guides/create-a-user-defined-function.md#ksqldb-how-to-create-a-udf), or look up critical information about them in the [reference documentation](../reference/user-defined-functions.md#ksqldb-reference-udfs).