How do you get your own seeds from your petunias?

Last year I successfully grew my own marigolds from seeds taken from my garden. Can I do this with Petunias? and how?

How do you get your own seeds from your petunias?
this is what i do,,cause Petunia seeds are difficult to grow...at the end of the season when the plants are dead i stuff the dead plants back into the pot they grew in and clover them for the winter and at spring time i pull the cover off and take out the old plant making sure to shake it well before removing the old plant..they will grow back in no time this way...
Reply:they will form in little pods , where the flower was ,they are very tiny and difficult to grow from seed without a greenhouse to start them in. i mean it can be done i grow all of my garden from seed, i just like the challenge ans watching them grow.
Reply:Leave the flowers on....don' deadhead them....reduce watering so that the plant is stressed and thinks it is dying....you will get your seeds.