There are literally thousands of dogs catbirds born everyday and when it's time your cat will know exactly what to do. It isn't a bad idea to take her to the vet but if you don't have the money theres not much you can do. Once the litter is weened take her to a low cost spay/neuter clinic so this doesn't happen again.
Gestation is the name for the length of a pregnancy. Gestation for a cat is anywhere from 60 to 67 days.
Signs of pregnancy, such as an enlarging belly begin to occur at five weeks.
I know that you have stated that you have no money to get to a vet but you should really try to save some money a vet visit in case your cat has a difficult delivery.
Care Credit is a low to no interest credit card that can only be used for veterinary, dental or other medical bills. You have a long time to pay it off. Please apply for a
Care Credit Card. Application is available online or at many vet's offices.
Alternatively, Please contact some local animal shelters in your area for low cost treatment. If you would like her to go through with the pregnancy it would be best if you are familiar with a no-kill shelter where the kittens can be brought to find them good homes and a place where you can get your cat spayed inexpensively after she weans the kittens.
The following web site from Claws and Paws Veterinary Hospital contains excellent information about what to expect during and after the pregnancy:
http://www.cpvh.com/Articles/37.html