By default, navs are left-aligned, but you can easily align them to center or right using flexbox utilities.
The following example uses the class .justify-content-center to align nav items to center.
Example
<nav class="nav justify-content-center">
<a href="#" class="nav-item nav-link active">Home</a>
<a href="#" class="nav-item nav-link">Profile</a>
<a href="#" class="nav-item nav-link">Messages</a>
<a href="#" class="nav-item nav-link disabled" tabindex="-1">Reports</a>
</nav>
— The output of the above example will look something like this:

Similarly, you can align nav items to right using the class .justify-content-end, like this:
Example
<nav class="nav justify-content-end">
<a href="#" class="nav-item nav-link active">Home</a>
<a href="#" class="nav-item nav-link">Profile</a>
<a href="#" class="nav-item nav-link">Messages</a>
<a href="#" class="nav-item nav-link disabled" tabindex="-1">Reports</a>
</nav>
— The output of the above example will look something like this:

Moreover, you can even vertically stack your nav items by changing the flex item direction with the class .flex-column. Also, if you want to stack your nav vertically on smaller viewports but not on others, use it with responsive breakpoint (e.g., .flex-sm-column).
Example
<nav class="nav flex-column">
<a href="#" class="nav-item nav-link active">Home</a>
<a href="#" class="nav-item nav-link">Profile</a>
<a href="#" class="nav-item nav-link">Messages</a>
<a href="#" class="nav-item nav-link disabled" tabindex="-1">Reports</a>
</nav>
— The output of the above example will look something like this:
