What is the difference between a "Stream" and "Flow" and when/how should you use each?

For what you describe, you'd want to go with a smart campaign (flow).

An engagement program (stream) is more like a continual conversation with a lead where you can keep adding content over time and move them across streams based on different criteria. You could probably manage what you're looking to do with an engagement program, but it'd be a lot harder than just doing a smart campaign.

Hey Angela,

A stream is just a list of prioritized content that will send based on whatever cadence you think is appropriate.

In the example you describe, setting up a Flow action in a smart campaign is probably the best way to go. I would recommend setting their Engagement Program Cadence to Paused after sending the follow-up email you're describing. That way, you ensure your reporting data is in tact, and have the opportunity to turn the engagement program on for that lead again in the future if it's merited. 

Hope that helps!

This does help alot! So would I set up only one Smart Campaign? Or would I set up a Active, Paused and Engaged Smart Camapign and would the flows are talk to each other (connect them somehow) or would I just set up one?

I'd say it depends on how complex you want to get with that kind of gatekeeper style Smart Campaign. For the scenario you mentioned, which essentially says, "If they engage, keep sending them stuff; if they don't engage, send them a note and pause engagement," you really only need the one Smart Campaign to filter people out. Everyone else is engaging with your content stream, so you can leave them alone (in that sense) to receive it.

Angela,

Use an Email Send or Email Blast Program for what you want. Then create the smart campaign to listen for the form fill out.

When people say "flow" here, they often mean Smart Campaign.

eg:

Program
-email 1
-email 2
-Smart Campaign (Flow) 1: Fills Out Form
--Send Email 1
--Wait
--Send Email 2

When you use an Engagement Program, that is when you can use Streams. This is only recommended for certain situations, which yours does not really seem to be. So you could use an Engagement if you had (or plan to have) several emails and content offers over time.

Then you would have a listen campaign (in either situation) that says "If Member of Smart List IS Not Clicked/Opened" then Remove from Smart Campaign 1. (or Move to Empty Stream).

Please review these slides:
http://www.slideshare.net/jdavidhill/marketo-engagements-and-drip-nurturing-boston-user-group-dec-10-2013