✅ (General Question) Using section

hi why do you use

using(FileStream stream = new FileStream("Document") {
  stream.thisIsJustAExample
}

using(FileStream stream = new FileStream("Document") {
  stream.thisIsJustAExample
}

using(FileStream stream = new FileStream("Document") {
  stream.thisIsJustAExample
}

using(FileStream stream = new FileStream("Document") {
  stream.thisIsJustAExample
}

what's the point of the Using section / structure?