I made some pages in Wordpress and displayed a navigation therefore the user can click to visit individuals pages.

Whenever you click the links, apart from the house link, it'll visit a 404 Page not Found Page and display a note because the one below:

The asked for URL /new_mtt/about-us-2 wasn't available on this server.

I recognized I do not possess a page.php file. Will I need that to be able to view pages apart from the index?

How come my pages no longer working properly?

There needs to be considered a .htaccess-file inside your Wordpress-directory. In there must be the guidelines for url spinning. The issue might be: that file is missing, the file is corrupt or mod_rewrite isn't permitted.

You almost certainly have to regenerate your permalinks -- that solves the issue around 90% of times. Click Configurations, Permalink then pick any option that isn't selected, hit Save, select the option you initially wanted again (likely a custom structure with %postname%), hit save again, and verify it saved.

Whether it can't save, just like the prior answer, make certain you make sure that your .htaccess file has global write access.