I get asked about Clipping Mask vs Alpha Lock in Procreate all the time, and I want to show you a breakdown of what both features do (and why you should always use Clipping Masks).
What do you use Clipping Mask and Alpha Lock for?
Clipping Mask and Alpha Lock are great tools to use if you want add more interest to your art without having to clean up the mess you might create along the way.

I have separated my layers by color for ease, and this will also allow me to apply a Clipping Mask and Alpha Lock easily on the area that I specifically want to enhance. Both Alpha Lock and Clipping Mask allow you to draw and add details to only the parts you want to.
How to apply Alpha Lock
There are two ways you can enable Alpha Lock. You can tap on layer and select Alpha Lock:
Or you could just swipe right on the layer you want to apply Alpha Lock to:

Once Alpha Lock is enabled, you'll see a checkerboard pattern behind your drawing.
Now, you can draw on top of your isolated element or section without worrying about messing up the rest of your drawing:

But, let's take it a step further and instead of using Alpha Lock, we'll switch to Clipping Mask, my preferred method.
How to Apply Clipping Mask
Step 1: Create a new layer
This layer should sit above the layer you want to work on - in my case, above the leaves.

Step 2: Enable Clipping Mask on the new layer
Tap on your new layer and select Clipping Mask from the flyout menu.

Once the Clipping Mask is applied, you will see a tiny arrow on the side of the layer you applied it to:
Now, it's play time!
Step 3: Add details
On the clipping mask layer, you can now add details, textures, or even a color fill that will impact only the layer underneath your Clipping Mask.

If you tap on your layer and deselect Clipping Mask, you will see all of the details that have gone beyond the area you want to work on (in my case, outside of the leaves).

This is where the difference between Alpha Lock and Clipping Mask comes in. Clipping Mask gives you the versatility to come back in any time and remove whatever you added on top, whether fully or partially, without impacting the layer underneath.
Bonus: Create another Clipping Mask
The fun doesn't stop here because you can layer Clipping Masks on top of each other for additional effects! Create another new layer above your current Clipping Mask layer, and enabled Clipping Mask. Now you can layer extra details without worrying about the outcome:

You can also move the layers around if you want to switch the hierarchy of your Clipping Masks!

Texture can really bring your art to life and give it that extra dimension.

Now you know the difference between Alpha Lock and Clipping Mask, which one will you be using the most?