Do Views execute underlying query everytime ??

Hi all,

I have like a repository table with is very very huge with atleast a few
hundreds of millions, may be over that. The information is stored in form of
rows in these tables. I need to make that information wide based on some
grouping and display them as columns on the screen.

I am thinking of having a solution where I create views for each screen,
which are just read only.

However, I donot know if the query that creates the view is executed
everytime I select something from the view. Because if that is the case,
then I think my queries will again be slow. But if that is the way views
work, then what would be the point in creating them ..

Any suggestions, helps --

(Please pardon if this question should not be on performance forum)

Thanks,
Amit