Tutorial on Creating a 2-Step Form

I have a client request to create a 2-step form

First form : capture name / email /message
push this info into Marketo and display a second form
Second form : Company / telephone

If the user submits the second form, it should augment the first form submission and post a thank you.
If not, the first set of data is already in the system.

Any help or guidance would be greatly appreciated. I'm pretty new to Marketo.