GRANT EXECUTE ON proc TO user

Or rather than granting permissions directly to users, it's probably
better than adding them roles, and then grant access to the role instead.

But note that just because you grant them access to run the procedures,
that does not mean that they can run the procedures successfully. They
will get SELECT, INSERT, DELETE and UPDATE permissions to tables referenced
by the stored procedures, if the tables and procedures have the same
owner. However, this so-called ownership chaining does not apply to
other statements such as CREATE/DROP TABLE (temp tables are OK) or
TRUNCATE TABLE.