what does container class do in bootstrap code example

Example 1: bootstrap container-fluid

Use .container-fluid for a full width container, spanning the entire width of the viewport.

<div class="container-fluid">
  ...
</div>

Example 2: container in bootstrap

Containers
Containers are the most basic layout element in Bootstrap and are required when using our default grid system. Choose from a responsive, fixed-width container (meaning its max-width changes at each breakpoint) or fluid-width (meaning it’s 100% wide all the time).
While containers can be nested, most layouts do not require a nested container.

Syntax:
<div class="container">
  <!-- Content here -->
</div>

Example 3: bootstrap container

Our default .container class is a responsive, fixed-width container, meaning its max-width changes at each breakpoint.

<div class="container">
  <!-- Content here -->
</div>

Example 4: container class in bootstrap

meaning it’s 100% wide all the time