E-mails. I can receive -mails but not send them they go into my sent box an stay there when I try

Question

I can receive -mails but not send them they go into my sent box an stay there when I try again to send them nothing happensm I would like to say I do not understand all the computer language but as a new user I am trying to understand it my computer is a Dell inspiron 1501 windows vista I would be very grateful for any help ( I would add that I am a silver surfer so not as fast as the young ones !