How to create indexes from array?

I want to create indexes to implement full text queries. The documentation from supabase helped me to create indexes for 2 columns with string values, but I would like to create indexes for 4 columns, but 2 of them are arrays, so my question is how I can create indexes for array.

Docs from supabase:

alter table
  books
add column
  fts tsvector generated always as (to_tsvector('english', description || ' ' || title)) stored;

create index books_fts on books using gin (fts); -- generate the index

select id, fts
from books;