What do you want to know about it?

how to do it

and maybr how to restrict user from entering anything they want

they always will be able to put anything they want ;) but, you can add logic to check for the [slug](https://nextjs.org/docs/app/building-your-application/routing/dynamic-routes#convention) to ensure it's rendering what you intended by, for example, using the slug to fetch from an external API:

// app/profile/[slug]/page.tsx

type Props = {
  params: Promise<{
    slug: string;
  }>;
}

export default fnuction ProfilePage({ params }: Props) {
  const slug = (await params).slug;
  
  // Fetch from an API (example)
  const response = await fetch(`https://api.something.com/profile/${slug}`, {
    // ...
  });
  // ...

  const { profile } = await res.json();

  if (!profile) {
    // Return JSX 
    // return <h1>Invalid</h1>
    
    // Return redirect
    // import { redirect } from 'next/navigation'
    // return redirect("/")
  }

  return <ProfileComponent profile={profile} />
}

this is just one example of a way to validate the route(s)