Private pages for users

There's also the method of going into a template's settings, Access tab, and checking "Enable HTTP Authentication". That checkbox, combined with the member groups you check to have access right above it can also password-protect certain templates.

Yes private pages are easily do-able. There are numerous approaches, here's one using a template to control who can view content.

Create a template and add some conditional tags to determine if the person is logged out (show login form), or logged in (show the content)

Assuming that anyone that is logged in can see content

{if logged_out}
  YOUR LOGIN FORM
{/if}

{if logged_in}
  YOUR PRIVATE CONTENT
{/if}

Only allow access to a specific member group

{if logged_out}
  YOUR LOGIN FORM
{/if}

<!-- only allow member group 5 to access content -->        
{if logged_in_group_id == "5"}
  YOUR PRIVATE CONTENT
{/if}

<!-- if logged in member group is not 5 -->
{if logged_in_group_id != "5"}
 You're logged in but not allowed to see content
{/if}

EE doc search works pretty well these days, and the info is all there.

Login and registration: https://docs.expressionengine.com/latest/member/index.html

Member groups: https://docs.expressionengine.com/latest/control-panel/member-manager.html#member-groups

Controlling access to templates: https://docs.expressionengine.com/latest/control-panel/template-manager.html#access