Q: how can i transfer contacts from my old phone(android) to my new iphone

One way to do it is via the sim card. If the sims cards are different size, the retail store of your cellular carrier can copy the contacts from your old phone's sim to a sim that will fit. More information: http://support.apple.com/kb/HT4994

Actually, tranferring via the SIM is not the best solution. Contacts copied to the SIM are generally just the primary number, and much other information such as notes, etc. are not copied. This can also result in multiple entries for the same individual and cause a lot of extra work once imported to the iPhone. Going from Android is generally handled better by making sure contacts are in the Gmail account and then syncing that to the iPhone. You can save the contacts that way. Just wanted to share that information with you. I wasn't sure if you had ever seen what contacts saved to a SIM look like when imported to the iPhone.

How do I save my contacts to my gmail?

You sync them to your gmail account.