Here is how to create a simple login form:

<form>
    <div class="form-group">
        <label for="emailAddress">Email Address</label>
        <input type="email" class="form-control" id="emailAddress" placeholder="jdoe@example.com">
    </div>
    <div class="form-group">
        <label for="passwordInput">Password</label>
        <input type="password" class="form-control" id="passwordInput">
    </div>
    <div class="form-group">
        <label class="form-check-label">
            <input type="checkbox" class="form-check-input">
            Remember me
        </label>
    </div>
    <button type="submit" class="button info filled">Submit</button>
</form>

Forms are made up of a collection of groups called form-group. Within each form-group is an optional label and a form-control. The form-control can be an <input>, <textarea>, or <select>. Use form-check-label within a form-group when creating a checkbox or radio.

form-control can come in 3 different sizes like so:

<div class="form-group">
    <input type="text" class="form-control large"> <!-- Large -->
    <input type="text" class="form-control"> <!-- Default -->
    <input type="text" class="form-control small"> <!-- Small -->
</div>

Finally, to create inline forms just add the form-inline class to the form element like so:

<form class="form-inline">
    <div class="form-group">
        <input type="email" class="form-control" placeholder="jdoe@example.com">
    </div>
    <div class="form-group">
        <input type="password" class="form-control" placeholder="Password">
    </div>
    <button type="submit" class="button info filled">Submit</button>
</form>