This is the 971st most frequent Spanish word.
necesarias
Necessary.
The word "necesarias" describes the essential attributes of "herramientas" (tools), agreeing in feminine plural.
Esas herramientas son necesarias para completar la tarea.
Those tools are necessary to complete the task.
Here, "necesarias" modifies "explicaciones" (explanations), consistent in feminine plural.
Las explicaciones necesarias fueron dadas para entender el tema.
The necessary explanations were given to understand the topic.
In this case, "necesarias" qualifies "medidas" (measures), also in feminine plural for agreement.