Why Review?

First, you don't have to be a lead or super experienced to review code! Reviewing code is a common practice in the industry and a useful skill to develop — why not start here?

Reviewing others' code:

Gives you visibility into other parts of your project
Allows you to learn, discuss, debate code standards/good practices
Is a path for you to improve communication skills, like giving effective feedback
Keeps the code in your project clean (useful for when you're building on top of other's code :))

There's also a way for you to just comment on others' code, allowing you to ask questions or give feedback without explicitly blocking the PR from merging.

TLDR; get involved with PRs!

What to Look For

There are a couple things to look for while doing code reviews. The obvious ones:

Code style. Generally enforced through linters, but try to keep variable names descriptive and consistent.
Bugs. Test the code yourself, especially if it's not something that can be tested with continuous integration (such as a design change). [add sth abt vercel/preview deployments]

Less obvious ones:

How well does the code fit into the repository? A good example of this is when someone writes a utility file for a feature that they are developing, but the utility file can be super useful for the other aspects of the project as well. Understanding how to surface functions like these can save a lot of time for future development.