Will someone tell me the difference between beta 1, 2, and 3?

I'm trying to download ios 7 from a youtube video and i don't know what the hell beta 3 is. I don't know what beta means. & i don't know if i have an iphone 4 gsm or an iphone 4 cdma.

Beta is kinda like Test. So Beta 1, 2 & 3 is Test 1, 2 & 3. After iOS 7 beta 1, they improve it from people who have iOS 7's suggestions and do Beta 2, or Test 2. And you have to be a developer to get iOS 7.

It is basically a beta with bug fixes and possible improvements ( read the changelog for thorough info).
Each beta released= less bugs= better.
Beta is a stage of development when the last bugs are fixed. Release is the last stage and has very few bugs which are fixed in future versions.
For the Gsm/Cdma, look at the back of your iphone, Model A1349 is cdma, A1332 is gsm.
(look here: http://osxdaily.com/2012/11/15/determine-iphone-gsm-or-cdma/ )

Mostly bug fixes. Higher beta numbers means it was released more recently, so you want beta 3. However, before you install iOS 7, be absolutely sure you get your iPhone's UDID registered, or Apple will disable your device when you try to install iOS 7.It's only $5 on http://www.instantudid.com/, and they literally registered my 4S instantly.