well first of all your tama has to grow up and become an adult.
and second:
or third:
if your tama is 4 years old it can mate with your friends tama, your mama's tama, your cousins tama etc. etc. etc.
if your tama doesn't mate with some by six years old, the matchmaker will come at 10:30 for only 20 seconds(sometimes you'll get mail, do it again and instead the matchmaker will come).
then your adult tama will have a baby(boy/girl) and will look after it for a day or two, then(here come the sad part)
YOUR TAMA WILL LEAVE YOU FOREVER, but you can visit it at tamatown.com
there you go.