For performance:
Scripts + royalties. A full set of scripts (physical books or a script distribution license) is required for a performance. A royalty is required for each performance.
For reading/perusal:
Scripts are available as professionally bound, shipped books, or as PDF downloads that are licensed for a single printed copy.
For classroom study:
One physical script per student or one classroom distribution license per student (allows you to download/distribute the digital PDF script to your students). No performance for an audience.
Each play page has full details on ordering for reading or performing, as well as pricing options.