When you create site collection via CSOM default Sharepoint groups (Visitors, Members and Owners) are not created by default. So when you will go to Site settings > People and groups most probably you will only see Everyone and Excel Services Viewers:
In order to create these groups you need to write additional code by yourself. Here it is:
After executing this code you will see 3 additional groups in Site settings > People and groups:
If you will go to Site settings > Site permissions you will find that Visitors group has Read permissions on the site, Members – Contribute and Owners – Full control:
Hope that this information will help you.