How do I add custom fields together

How do I add custom fields together

Hi there!

I am new to ZOHO CRM and this may be a novice question...

I work for a trash company and my sales team sells various types of trash services (Bins, compactors, construction bins) to commercial businesses and there are multiple fields that I can create to associate with our services.

Do I add these fields to the account page layout sections? If so, how do I get these fields to add up to a sum total?

Or instead of creating fields that correspond to our services, should I create our various services (like products) and then have my reps select the services once in the proposal section?

Thanks for your help!

-Rochelle