Did you make sure you have reference to bootstrap (i.e. bootstrap.min.css) in the head?
Next, you have first element with col size of 8 and only one of the reamining two fields will fit into one row.
Also, the '< br/>' after the first field is probably not needed. The following update to your code puts three fields into 1 row (as I updated col size to 4 for the first field and removed the '< br />' and added a reference to bootstrap cdn.
<html>
<head>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.0/css/bootstrap.min.css">
</head>
<body>
<form method="post" action="example.php">
<div class="form-group-row">
<div class="col-xs-4 col-sm-4 col-md-4 col-lg-4">
<input class="form-control" type="text" placeholder="Name" name="name">
</div>
</div>
<div class="form-group-row">
<div class="col-xs-4 col-sm-4 col-md-4 col-lg-4">
<input class="form-control" type="text" placeholder="example" name="example">
</div>
<div class="col-xs-4 col-sm-4 col-md-4 col-lg-4">
<input class="form-control" type="text" placeholder="example" name="example">
</div>
</div>
</form>
</body>
</html>