Hi Nikki,
For your first question, when you add your custom field to a report, you should see under Column Settings, the ability to Sum the column. Select Sum and now your custom field column will be totaled, but remember to add a Grouping to your report for the aggregate totals to render. For your second question, let's say your first custom field is called "ABC" and your second custom field is called "XYZ". To get a combined total for these two fields, you would add another column to your report, Switch to Text Mode, and add in the following:
displayname=Name the Column Whatever You Want
valueexpression= SUM({DE:ABC},{DE:XYZ})
valueformat=customNumberAsString
(The DE: in this case is letting Workfront know that this is a custom field vs an out-of-the-box field.) The above will give you the combined total for the two fields.
Alternatively, you could create a calculated field on a custom form to get this combined number, and then pull in that field onto reports.
Hang in there with reporting…there are lots of good articles on Workfront Support and training videos/session in Workfront Ascent. I recommend taking the reporting classes, and if you get stuck on anything, there are many people in the Community that are ready to lend a hand and help out when needed to figure things out. Terry Hynd EBSCO Information Services