How is this done?

Excel is not a database, it is a spreadsheet.

Access is a Database much like Oracle, MySQL, or Postgres. Though, I would not put Access in nearly the same ballpark.

So, on to your question.

This script has two parts, and is fairly complex, so try to stick with me

First the HTML form itself. There is some magic going on here. Notice how all the fields arent available at the start. As you pick the first element, the available options appear for only that first selection. At each phase, a call from Javascript back to the server end requests the available options for the next step with what was already entered. The server side script then asks the database something like .. (in plain english)

select for me the 'z' tire information from the tires table where the user has selected 'x' and 'y' already

in database language it may look something like

select t.size from tires t where t.width = '30' and profile = 0;

The server then responds back to the javascript code and updates the drop down with only the proper selections (noticed the pause in between selecting different options), when the next selectionis made, another call to the server is made.

When the user is finished, this form is then submit back to the server all "complete" to do a search on the tires that match all the criteria. The server again calls the database to get a list of all tires that match, and the server code then is built so that it can display the proper HTML that the browser can understand.

These systems, can be somewhat complex, but are pretty trivial for an experienced programmer.