First login to your sites admin dashboard. 

Then navigate to the left hand side and find the tab "Appearance"

Then choose "Customize" 

Once on the customization page, select the tab "Widgets"

You will then want to choose a page such as a category page, or shop page, something that has a sidebar to edit.

Once on the page you will choose "sidebar" to edit and you'll be able to see the changes in real time. (each widget correlates to a sidebar widget as shown in black outline in photo below)

To add a new block go to the bottom of the widgets and hit "Add Block"

In the search bar type "stock"

Choose widget "Produdct Filter - Stock"

You will see the widget added to the sidebar

You're able to move the widget and reorder them as you'd like by either dragging or using the arrows. 

Once you're happy with it's location you will need to hit "Publish". 

That completes this tutorial. Thank you!