Materialized view are totally different from views. They used to be called "snapshots", which was a more descriptive name. They store a snapshot of data as it exists at a moment in time, and need to be periodically refreshed. The advantage is that the results of an "expensive" query can be "materialized" (stored) to be used by other queries. For example:
create materialized view dep_sal_mv as
select deptno, sum(sal) as sumsal
group by deptno;
This MV could be used by the optimizer to speed up a query that required salaries summed to department level such as:
select sum(sal) from dept where deptno = 10;
There is a lot more to it than we could cover here, so I'll refer to you the docs at this point.