I'm an Apex and Visualforce newbie who could use some advice from the developer community to figure out how to allow someone who is not logged into Salesforce to submit an update to an existing record on a custom object.

Context: The non-profit I work for (Boundless Brilliance) sends a pair of female college students who are majoring in a STEM subject (STEM=Science, Technology, Engineering, Mathematics) into an elementary school classroom to give a fun and educational STEM presentation and hands-on lab. The mission is to get elementary school students -- especially girls -- excited about STEM subjects at an early age. 

These are the two steps in the process along with my initial thoughts on how this could work:

1. A record is manually created on a custom object labeled "Volunteer Hours". This record contains fields with information about a presentation, such as date, location, type of presentation, name of volunteer, etc...

Some of the information about the presentation will not be known until afterwards, such as Hours Worked, Presentation Effectiveness, and Transportation Cost. These fields and 8 others like it are left empty when the record is created. They will instead be updated by the volunteer after the presentation is complete.

2. After a presentation is completed, the volunteer will submit a form on a Visualforce page that includes typed-in or selected values for "Hours Worked", "Presentation Effectiveness", "Transportation Cost", and the 8 other such fields.

Each record on the Volunteer Hours object has an "HoursID", which contains a unique number as a record identifier. The volunteer can submit that number with the rest of the form data so Salesforce can identify the corresponding record and update the fields accordingly.

So my approach to building the form on the Visualforce page depends on this procedural question:

Can the new user-input data plus the "lookup data" HoursID all be submitted at the same time to the Volunteer Hours object using a form on a Visualforce page? 

OR 

Does the volunteer need to first submit the HoursID to establish some type of connection to the appropriate record that does not require loggin in, and then as a second separate step submit the updated values for the user-input fields?

OR

Is this not possible?

There are a couple of apps in the AppExchange that seem to be able to do this, but they are prohibitively expensive for our little non-profit.

Any comments or suggestions are appreciated. Thanks!

I am trying to go through the "Get Started with the Salesforce Platform" trail. In this trail we create the DreamHouse app to use throughout the trail  I have successfully installed the App.  The next step is to "Click the Data Import tab and click Initialize Sample Data".  I have tried this repeatedly over the last couple of days and it will not import.  When I click on "Initialize Sample Data" it just hangs until I shut it down - have let it go for 30 minutes and still just hangs.  No error message or anything else.
 

Any idea how to get this to initialize so I can get on with seeing this app and moving on in the trail?