The new Gmail inbox splits the inbox views in different tabs like Social, Promotions, Updates and so on.
While this may be useful, it often can be bit time consuming to navigate to each of these tabs and see the messages listed under them instead of the default view. Besides that, the new inbox split view serves ads via emails (Promotions section) which may be not everyone wants to see every time they check for emails.
So, in order to revert the inbox to it’s default view :
1. Click on the gear icon in Gmail and select “Configure inbox”.
2. Under the section “Select tabs to enable”, deselect all the categories (the “Primary” category can’t be deselected).
3. Hit “Save”.
All done. The Gmail inbox will now be restored to it’s earlier non-tab view as before.