Liquid locking basics
Locksmith has a feature to create "Liquid" locks, which allows you to lock pages in your store that are otherwise not searchable using the basic "Add lock" resource search in Locksmith.
Note: this is an advanced guide that requires knowledge of Shopify's Liquid language. If you're a developer type, read on! If that is not you, and you aren't finding what you're looking for in the Locksmith app, please feel free to contact us via email at [email protected]
Moving on - to begin, press the "Start a Liquid lock" link:

This will bring up the following form:

The "Liquid condition" is the condition that is evaluated to decide if the lock will be engaged on the current page. The Liquid condition simply needs to evaluate to true or false.
Useful examples
Any condition that evaluates to true will result in a locked page. So, imagine if you created a lock with this condition:
{% if true %}
That would result in every single page in your store becoming locked. This isn't advisable, it's just a proof of concept :)
One of the most useful variables that you can use is the canonical_url variable. This variable contains the full url of the current page, so it is a good way to lock pages that aren't usually searchable. For example you have an app that lives at my-store.myshopify.com/apps/bulk-order-form-app, you could lock it with the following condition:
{% if canonical_url contains "apps/bulk-order-form-app" %}