a user inputs triangles and they have to display

i want to draw some triangles.
the user inserts an triangle and the new triangle has to display with the other ones.
i want to pick the triangles.

how can i do that, to draw all the triangles the user has actualy selected.
also to pick

what you need to do is assign a boolean variable to each triangle to know if it is visible or not. To select a specific triangle use gluPickMatrix. There are some samples here in the discussion forums.