if we use nokia lumia, we cannot download facebook instead we can go search Basic Browser facebook so we can use the app?

What do you mean?

I use Microsoft Lumias, 950 now, 950XL again soon.

The Store no longer has a Facebook App for WP, but they have alternative Apps that look to be Facebook App clones. To use these, go to Store from WP and search for Facebook.

The Edge connection to Facebook works just fine, despite the warnings posted about the browser on some pages. So, start Edge, go to facebook.com, log in, navigate to the page you want to be your Facebook Home screen, then select the three dots, bottom right and select Send to Start.

This is now your Facebook app and will have the Facebook logo!

Browser is your only option just use your edge and type fb.com and use it coz Facebook doesn't support windows phone.

Goto Facebook.com and login using Microsoft Edge, then add Facebook as a start screen shortcut although I'm not sure if EdgeHTML supports PWAs (Progressive Web Apps) [which is the browser engine on Windows 10 Mobile and the Xbox One games console (unless they updated it to the blink (chromium) engine?)] so the page will just be a website shortcut...

Alternatively you could flash a copy of Windows 10 or Windows 11 to your Windows 10 Mobile device and use Facebook that way (in a browser or the Windows 10/11 UWP app) by following some online guides at your own risk although I don't know if these can run on Lumia 600-series devices