Org-Wide default defines baseline level of access that the most restricted users should have. This is to safeguard your data and use other record level security and sharing tools to share data with other users.
How to access Org-Wide default.
Step 1. Login into your salesforce org.
Step 2. Go to Setup.
Step 3. In Quick Search, Type “Sharing Setting”. Select Sharing Setting.

There are basically 5 different sharing levels that you can choose for each object.
- Private
- Public Read Only
- Public Read/Write
- Controlled by Parent
- Public Read/Write/Transfer