Why I can't create or edit news?

If you can't create news you don't have permissions. By Default all users can only read news. 

Ask your system admin to change your permissions. 

It can be changed in Settings: Permissions. 

Choose your role. Click on edit icon. 

In new window click on tab Role Resources. 

Update permissions:

Manage News = you can create and edit news. 

Delete News - you can remove news. 

Save permissions.