I have an individual that needs to update site pages on a site collection. In order to update the site pages should place them in a SharePoint group with Edit or Contribute permissions.
Contribute permissions has "Read" permissions, plus:
- Add Items
- Edit Items
- Delete Items
- Delete Versions
- Browse Directories
- Edit Personal User Information
- Manage Personal Views
- Add/Remove Personal Web Parts
- Update Personal Web Parts
For your requirements to update the site pages, "Contribute" permissions are enough. You can grant "Edit" permissions only if user needs to make any changes at list/library level - changing site pages library settings, etc.
Documentation: User permissions and permission levels in SharePoint
Regarding the content of permissions, you can go to Site Permissions-->Permission Levels, and you can see the existing Permission Levels in your site. Among them, Contribute and Edit belong to the default Permission Level. You can directly click on them to view the specific permissions contained in them (it is recommended not to modify them. If necessary, you can create a new one through Add a Permission Level). Then select the required Permission Level according to your needs. Regarding the issue of permissions, you can go to Site Permissions-->Grant Permissions, give the group the permissions you want, and then add the user to that group through Grant permissions.
For more details, please refer to: https://learn.microsoft.com/en-us/sharepoint/understanding-permission-levels