I want to get an iPhone, now what?

Let me just say I am completely new to this whole "smart phone" thing. I've had my trusty little flip phone for about 8 years, and now I finally think it's about done for. I want to get an iPhone, but I have no idea what to look for, what all this iPhone 4 or 5 or 6 business is or what it means, and what plan to get. If anyone knows the inside and out of these little phones and doesn't mind helping an old fashioned lady out, I'd really appreciate it. I need a relatively inexpensive plan that will allow me to do what I need to do (get on the internet, check emails, etc.) A few friends of mine said something about group chat, does that come with it or is that an app(?) you download or something? Oh and they mentioned the cloud. What is that? Clearly, I am lost on this subject. Thanks to all that can help!

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