Lightswitch fields give you a simple toggle input for times when all you need is a “Yes” or “No” answer.
This field will either return a 1 or 0 from the database, so you can test if it is in the on position from a template like so:
{% if entry.lightswitchFieldHandle %}
<p>I'm on!</p>
{% else %}
<p>I'm off.</p>
{% endif %}