It sounds like you haven't gone through Foundation Training, which teaches the basics of things like Collection Manipulation. You may want to reach out for training because even with Blue Prism, it's typically not a good idea to develop without having been trained on how to use it.
The short answer for now, though, is that you'll probably want to use Loop stages, choose the collection name inside the loop stage start, and then use calculation stages or multicalculation stages inside the loop with expressions such as [CollectionName.FieldName] to get the values.
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Dave Morris
Cano Ai
Atlanta, GA
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Dave Morris, 3Ci at Southern Company