From php web to wordpress conversion, href changes only in URL

I have converted my PHP dynamic website into WordPress. Whole design is perfect. But unfortunately, when I click on any href link. it just changes in URL but not displaying the related linked page. Following images clarify more good:

When Clicking on link addDegree.php From sidebar nav:

li class="nav-item" data-toggle="tooltip" data-placement="right" title="Degree Pages"
          a class="nav-link nav-link-collapse collapsed" data-toggle="collapse" href="#collapseDegreePages" data-parent="#exampleAccordion"
            i class="fa fa-graduation-cap" style="color:gray;"/i
            span class="nav-link-text"Degree Management/span
          /a
          ul class="sidenav-second-level collapse" id="collapseDegreePages"
            li
              a href="addDegree.php"Add New Degree/a
            /li
            li
              a href="viewDegrees.php"View All Degrees/a
            /li
          /ul
        /li

As in image:

See URL in below image:

Please help me to resolve this issue. Thanks!