A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Manevax,
By saying "inside the company":
If you'd like to restrict only the users/accounts in your Office 365 tenant can access SharePoint Online, which means "to disable external user access", you can refer to:
Turn external sharing on or off for SharePoint Online
If you mean how to restrict users' SharePoint access outside of your company's local domain/network, you may check the following:
Office 365 URLs and IP address ranges or
Setup SharePoint Online & On-Premises Single-Sign-on (SSO)
Thanks,
Jim