Hi, 
Inventory Overview is supposed to show you an overview of what you have currently in your operations. 
For example, In the following screenshot, Odoo tells the user that: 



1- you have 4 late receipts to process and that you have to manage.
2- 0 Internal transfer
3- and so on...

And this is the purpose of an "Overview"
Once you click on 4 receipts for instance, that's where you can check your incoming pickings, update them, create new ones ...

For Operation Types, you need to go to Settings => Operation types if you want to update/create/delete..

This is what Odoo offers as basic functionnalities. You may find other modules that add buttons to Inventory Overview. Nevertheless, the main purpose of this menu is to present your pickings per type.

hope this helps.