As other said, it does help you gain more perspective.

However, since you mentioned that you are new and never reviewed before :

• My suggestion would also be to take as much time as you need to review the papers (I took days initially as I would read the paper multiple times and will also read relevant citations).
• If you really think you didn't get some part in the paper even after you tried reading the background. You can always tell this in reviewer discussion section, this will help meta-reviewer and other reviewers to look at that section.
• There are blogs and even videos on how to do a good review.
• Think that someone like you will receive this review, so think if you were in their place will the review you are providing be helpful.
• Lastly, please go through the guidelines.