How do you retrieve data from a dataset for later calculation?

I have a multistep form. On page 1, the user is required to pick services fed from a database into a dropdown. On page 2, the user enters their personal info. On page 3, I want to implement a “shopping cart”. Basically, a text box that will show the services picked (max is 4) and the sum of the selected totals.

What I want it to do is recognize which selection was picked from the dropdown, paste that to the text box, then get the corresponding price from the same row/different column stored so it can be summed later. Any help would be much appreciated. I’m new to this and don’t really even know where to start. The Wix help sites are too vague for me to understand and apply how I need it.

Check here → https://www.wix.com/corvid/reference/wix-storage/session
https://www.wix.com/corvid/reference/wix-data/wixdataquery/eq

I have read all of these and don’t understand how to use them.