What function would I create?

dI have created an invoice where I input information for more than 1
provider. I have "Provider" and "Hours". I also have linked certain cells
with other cells in the invoice. The first page is the Summary of all
charges, with the second page detailing the charges. How do I have it so that
XXX's number of hours links to the correct cell on the first page summary?
E.g., XXX is the provider, with 5.0 hours.
XYZ, is another provider with 2.25 hours. I may have multiple entries for
each provider on the details page. How can the running total link to the
summary page where I have each providers row with total number of hours for
each times their hourly charge? So basically I am asking if I input a
particular person in provider and the hours worked for that day, how can I
link it to the summary page as a running total?