How to create a flexfield index

Summary:

Need to understand how to create indexes on flexfields.

Content (please ensure you mask any confidential information):
The Fusion SaaS documentation makes reference to creating indexes on flexfields.

See for example:

"For best performance, you should create indexes for these four tables: […]"

as well as:

"A database administrator must create an index on the segment column representing the indexed attribute."

Please clarify if this documentation is incorrect, or else document the steps we can do as a SaaS admin to create such indexes.

Version (include the version you are using, if applicable):
24D