Posting Custom Fields to HTML from Wordpress - html

Question

I'm using a free shopping cart template called Roman Cart (https://romancart.com).
Per their documentation, they have the ability to post customer details to the cart (https://www.romancart.com/shopping-cart/how-it-works-examples/#aa).
But unfortunately, me being a newbie, am trying to figure out how and where I should use this? Should I be sending the customer details along with the tag I use to add items to the shopping cart?
<form action="https://www.romancart.com/cart.asp" method="post"><input type="submit" value="Add to Order"><br>
<input type="hidden" name="price" value="670.8">
<input type="hidden" name="storeid" value="10000">
<input type="hidden" name="quantity" value="1">
<input type="hidden" name="itemname" value="Pirinho"><br>Include Sample
<select name="itemname2"required oninvalid="this.setCustomValidity('Select Sample Preference')" oninput="this.setCustomValidity('')" >
Include sample
<option value="">-Select-</option>
<option value="Sample Preference: Green {15.00}">Green (+$)</option>
<option value="Sample Preference: Roasted {15.00}">Roasted (+$)</option>
</select><br></form>
So to send customer details, should I start using it like this?
<input type="hidden" name="CompanyName" value="ACME">
Also, I use Wordpress for people to register. How can I get the current_user information and send it alon with the tag?
<input type="hidden" name="CompanyName" value="wp_get_current_user();echo 'Company Name'">
I'm pretty sure the above is incorrect and there is a better way to execute this. Can somebody please help me? I will be forever so grateful
Thanks a million!