HTML

bootstrap 5 input group

<div class="input-group mb-3">
  <input type="text" class="form-control" placeholder="Recipient's username" aria-label="Recipient's username" aria-describedby="button-addon2">
  <button class="btn btn-outline-secondary" type="button" id="button-addon2">Button</button>
</div>

input button group

<div class="input-group mb-3">
  <div class="input-group-prepend">
    <button class="btn btn-outline-secondary" type="button"><i class="fa fa-right-arrow"></i></button>
  </div>
  <input type="text" class="form-control" placeholder="" aria-label="" aria-describedby="basic-addon1">
</div>

<div class="input-group mb-3">
  <input type="text" class="form-control" placeholder="Recipient's username" aria-label="Recipient's username" aria-describedby="basic-addon2">
  <div class="input-group-append">
    <button class="btn btn-outline-secondary" type="button">Button</button>
  </div>
</div>

<div class="input-group mb-3">
  <div class="input-group-prepend">
    <button class="btn btn-outline-secondary" type="button">Button</button>
    <button class="btn btn-outline-secondary" type="button">Button</button>
  </div>
  <input type="text" class="form-control" placeholder="" aria-label="" aria-describedby="basic-addon1">
</div>

<div class="input-group">
  <input type="text" class="form-control" placeholder="Recipient's username" aria-label="Recipient's username" aria-describedby="basic-addon2">
  <div class="input-group-append">
    <button class="btn btn-outline-secondary" type="button">Button</button>
    <button class="btn btn-outline-secondary" type="button">Button</button>
  </div>
</div>

group inputs html

<form>
  <fieldset>
     <legend>1st field set:</legend>
     Field one:<br>
     <input type="text"><br>
     Field two:<br>
     <input type="text"><br>
  </fieldset><br>
  <fieldset>
     <legend>2nd field set:</legend>
     Field three:<br>
     <input type="text"><br>
     Field four:<br>
     <input type="text"><br>
  </fieldset><br>
  <input type="submit" value="Submit">
</form>

input group

<div class="input-group mb-3">
  <button class="btn btn-outline-secondary" type="button" id="button-addon1">Button</button>
  <input type="text" class="form-control" placeholder="" aria-label="Example text with button addon" aria-describedby="button-addon1">
</div>

<div class="input-group mb-3">
  <input type="text" class="form-control" placeholder="Recipient's username" aria-label="Recipient's username" aria-describedby="button-addon2">
  <button class="btn btn-outline-secondary" type="button" id="button-addon2">Button</button>
</div>

<div class="input-group mb-3">
  <button class="btn btn-outline-secondary" type="button">Button</button>
  <button class="btn btn-outline-secondary" type="button">Button</button>
  <input type="text" class="form-control" placeholder="" aria-label="Example text with two button addons">
</div>

<div class="input-group">
  <input type="text" class="form-control" placeholder="Recipient's username" aria-label="Recipient's username with two button addons">
  <button class="btn btn-outline-secondary" type="button">Button</button>
  <button class="btn btn-outline-secondary" type="button">Button</button>
</div>

input groups

<form role="form" class="form-horizontal">
<div class="mb-15 row">
<label class="col-sm-2 col-form-label" for="example-input-small">Small</label>
<div class="col-sm-10">
    <input type="text" id="example-input-small" name="example-input-small"
        class="form-control form-control-sm" placeholder=".input-sm">
</div>
</div>

<div class="mb-15 row">
<label class="col-sm-2 col-form-label" for="example-input-normal">Normal</label>
<div class="col-sm-10">
    <input type="text" id="example-input-normal" name="example-input-normal"
        class="form-control" placeholder="Normal">
</div>
</div>

<div class="mb-15 row">
<label class="col-sm-2 col-form-label" for="example-input-large">Large</label>
<div class="col-sm-10">
    <input type="text" id="example-input-large" name="example-input-large"
        class="form-control form-control-lg" placeholder=".input-lg">
</div>
</div>

<div class="mb-15 row">
<label class="col-sm-2 col-form-label">Grid Sizes</label>
<div class="col-sm-4">
    <input type="text" class="form-control" placeholder=".col-sm-4">
</div>
</div>

<div class="mb-15 row">
<label class="col-sm-2 col-form-label">Static</label>
<div class="col-sm-10">
    <div class="input-group">

        <span class="input-group-text" id="basic-addon1">@</span>

        <input type="text" class="form-control" placeholder="Username" aria-label="Username"
            aria-describedby="basic-addon1">
    </div>
</div>
</div>

<div class="mb-15 row">
<label class="col-sm-2 col-form-label">Dropdowns</label>
<div class="col-sm-10">
    <div class="input-group mb-3">
        
            <button class="btn btn-primary  dropdown-toggle" type="button"
                data-toggle="dropdown" aria-haspopup="true"
                aria-expanded="false">Dropdown</button>
            <div class="dropdown-menu">
                <a class="dropdown-item" href="#">Action</a>
                <a class="dropdown-item" href="#">Another action</a>
                <a class="dropdown-item" href="#">Something else here</a>
                <div role="separator" class="dropdown-divider"></div>
                <a class="dropdown-item" href="#">Separated link</a>
            </div>
        
        <input type="text" class="form-control" placeholder="" aria-label=""
            aria-describedby="basic-addon1">
    </div>

</div>
</div>

<div class="mb-15 row mb-0">
<label class="col-sm-2 col-form-label">Buttons</label>
<div class="col-sm-10">
    <div class="input-group">
        <input type="text" class="form-control" placeholder="Recipient's username"
            aria-label="Recipient's username" aria-describedby="basic-addon2">
        
            <button class="btn btn-dark" type="button">Button</button>
        
    </div>
</div>
</div>

</form>