I have a pregnant chihuaha , its her first time and I need to know what to expect and
How can I help her when she is giving birth

Well there is SO much that you should really talk to a vet and an experienced breeder.
First I would suggest getting her on a good quality dog food. During the first 30 days of pregnancy she can eat her normal diet, as long as it is a high quality food. During the last month of pregnancy start switching her over to a high quality puppy food, make the diet change over a weeks time. Try and walk her daily. Excersise is really important. You don't want her to get too over weight. Talk to your vet about calcium suppliments, if the puppy chow is one of the better qualities, then you may not need to suppliment. Also talk to your vet about vaccines, some vaccines can cause abortions. Make sure to keep checking her temp. A normal dog temperature will be 100.5 - 102.5, about 24 hours before whelping her temperature will drop a few degrees.
Also when she is about to whelp do NOT leave her, many times a dog will need help with this, in a lot of small dogs c-sections are nessesary.
When you take your dog in for her vet visit, the vet will give you lots of info and help. Read up on making a whelping box, and how to properly care for your pregnant dog.
You can gether spayed right after she is finished nursing.

This is a helpful website.

Pregnancy & Birth in Dogs - whelping and breeding information

But you should probably think about getting some books as well.

You need to go to your vet and get info. Chihuahuas are prone to needing c-sections. This will not be a cheap procedure.

Chihuahuas are funny dogs

n15, I'm sorry but this is a serious Question and Answer site.
People come on here looking accurate advice.

If you are looking for a chat site this is not the place.