SQL & PL/SQL

Hi again,

I wanna know if it's possible having calculated fields in Oracle.
let's say i have a table which stores the marks of a class into a school. i wanna calculate the average of all these marks. of course, one note should be the thesis, so i mark into a field the statute of that mark (thesis mark or normal mark). i'll work with forms, but first i wanna know how can i obtain an average of these marks, and how should i store this information

Thank you :)