Configuration issue

[MariCalde]

Hi all, 

I have and issue, maybe I change a configuration or something and now the display of my SharePoint is not ok. For example: 

1. I go to site setting and it is display like the attachment.

 As you can see is not the common layout and the top links are actually the ones that are displayed in the left hand side of the page, I am not able to edit the links that were on the tp. 

2.  When I try on my home page to edit the left hand side menu, clicking on the +, it opens a new window with the configuration as classis mode. 

I don't really know what is happening, really appreciate your help! 

[#2]

So this is a really a Classic SharePoint Site which is not connected to an Office 365 Group the one you are familiar with having a left navigation.

So basically you can Convert/connect the Classic site to a Modern SharePoint site which is connected to M365 group and it also can have its own Team inside Microsoft Teams where you can access all the files or put a tab of the SharePoint look into one of the channels.

on the gear icon it will say something like connect to Microsoft 365 if you are the Owner of that SharePoint site and if that option is not blocked from your Organization.

[#3]

@PDostiyar thanks for you reply! Actually the home site is showing the left navigation bar but the configuration of the whole SharePoint is the problem. When I started this SharePoint, the configuration was as usual, but I think I changed some configuration, not sure which one!