PepsiChic

The lettr of intent is a letter you write to confirm that you and yoru US fiancee will indeed marry within the 90 day limit on the K1 visa. (if you have wedding details, venues etc you can post that, or if you know family will be going over etc). you need to sign it before you send it to your fiancee with your G325a.

Your US fiancee needs the letter to include with the I-129F package, when she gets it she also needs to sign it.

then for the K1 visa part you will need to update that letter with any additional wedding info etc and both sign it again. so this time get her to write it and sign it and send to you.

The I-134 (affidavit of support) is a form that your US fiancee, or other sponsor if she doesnt make enough money, sends to you for your K1 interview. Its a form that shows the government that someone in the US has enough money to support you and that you wont need/use government aid (like medicade etc).