You must show in that you have explicitly evaluated your sources. In your report you will mention which sources you have used, how they helped you and how you know they are credible/reliable. You should also have evidence of source evaluation in your appendix. How you choose to evaluate the source is up to you.
Here are some ideas and links:
ACCESS FM (analysing existing products - products are a type of source!)
CARS checklist (evaluating online sources)
CRAAP Worksheet (possible worksheet for process journal)
Evaluating Print Sources (checklist)
Evaluating Sources - Questions to Ask (possible worksheet for process journal)
Source Evaluation Table (possible worksheet for process journal)