Check out example codes for "bootstrap forms". It will help you in understanding the concepts better.

Code Example 1

<form>
  <div class="row">
    <div class="col">
      
  <input type="text" class="form-control" id="email" placeholder="Enter email" 
  name="email">
    </div>
    <div 
  class="col">
      <input type="password" 
  class="form-control" placeholder="Enter password" name="pswd">
    
  </div>
  </div>
</form>

Code Example 2

<!-- Default form login -->
<form class="text-center border border-light p-5" action="#!">

    <p class="h4 mb-4">Sign in</p>

    <!-- Email -->
    <input type="email" id="defaultLoginFormEmail" class="form-control mb-4" placeholder="E-mail">

    <!-- Password -->
    <input type="password" id="defaultLoginFormPassword" class="form-control mb-4" placeholder="Password">

    <div class="d-flex justify-content-around">
        <div>
            <!-- Remember me -->
            <div class="custom-control custom-checkbox">
                <input type="checkbox" class="custom-control-input" id="defaultLoginFormRemember">
                <label class="custom-control-label" for="defaultLoginFormRemember">Remember me</label>
            </div>
        </div>
        <div>
            <!-- Forgot password -->
            <a href="">Forgot password?</a>
        </div>
    </div>

    <!-- Sign in button -->
    <button class="btn btn-info btn-block my-4" type="submit">Sign in</button>

    <!-- Register -->
    <p>Not a member?
        <a href="">Register</a>
    </p>

    <!-- Social login -->
    <p>or sign in with:</p>

    <a href="#" class="mx-2" role="button"><i class="fab fa-facebook-f light-blue-text"></i></a>
    <a href="#" class="mx-2" role="button"><i class="fab fa-twitter light-blue-text"></i></a>
    <a href="#" class="mx-2" role="button"><i class="fab fa-linkedin-in light-blue-text"></i></a>
    <a href="#" class="mx-2" role="button"><i class="fab fa-github light-blue-text"></i></a>

</form>
<!-- Default form login -->

Code Example 3

<form>
  <div class="form-group row">
    <label for="staticEmail" class="col-sm-2 col-form-label">Email</label>
    <div class="col-sm-10">
      <input type="text" readonly class="form-control-plaintext" id="staticEmail" value="[email protected]">
    </div>
  </div>
  <div class="form-group row">
    <label for="inputPassword" class="col-sm-2 col-form-label">Password</label>
    <div class="col-sm-10">
      <input type="password" class="form-control" id="inputPassword" placeholder="Password">
    </div>
  </div>
</form>

Code Example 4

<form>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="Enter email">
    <small id="emailHelp" class="form-text text-muted">We'll never share your email with anyone else.</small>
  </div>
  <div class="form-group">
    <label for="exampleInputPassword1">Password</label>
    <input type="password" class="form-control" id="exampleInputPassword1" placeholder="Password">
  </div>
  <div class="form-group form-check">
    <input type="checkbox" class="form-check-input" id="exampleCheck1">
    <label class="form-check-label" for="exampleCheck1">Check me out</label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

Code Example 5

<form action="/action_page.php">
  <div class="form-group">
    <label for="email">Email address:</label>
    <input type="email" class="form-control" id="email">
  </div>
  <div class="form-group">
    <label for="pwd">Password:</label>
    <input type="password" class="form-control" id="pwd">
  </div>
  <div class="checkbox">
    <label><input type="checkbox"> Remember me</label>
  </div>
  <button type="submit" class="btn btn-default">Submit</button>

 </form>

Code Example 6

<form>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="Enter email">
    <small id="emailHelp" class="form-text text-muted">We'll never share your email with anyone else.</small>
  </div>
  <div class="form-group">
    <label for="exampleInputPassword1">Password</label>
    <input type="password" class="form-control" id="exampleInputPassword1" placeholder="Password">
  </div>
  <div class="form-check">
    <input type="checkbox" class="form-check-input" id="exampleCheck1">
    <label class="form-check-label" for="exampleCheck1">Check me out</label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

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