This is the standard language for GitHub-based authorization. We tried to customize it, but that is an unchangeable setting.
So what does it mean for you?
Sema uses GitHub credentials for your Sema account. With your Sema account, you have access to the Sema Chrome Extension to augment code reviews, and you have access to the Sema dashboard.
Here's GitHub's current answer about this:
Because of the way GitHub Apps work for this sign-in-as scenario (or other user-to-server applications), it has the ability to act on your behalf or know which resources you can access, but only within the scope of the permissions we’ve requested, in other words verifying your identity and reading your account’s email address.
We understand that this is poorly and confusingly worded for this kind of scenario. We’ve given this feedback to the team that is responsible for how this dialog is designed. We’ll be working with them to improve it to hopefully make it more clear and understandable as to what exactly is being requested so that you can be more confident in the decision you’re being asked to make.