How to enable product attribute swatches.

First please activate WCBoost - Variation Swatches plugin. Then go to the Products -> Attributes section and select attribute for edit  and select swatch type for it (Color, for example)

Then configure terms for current attribute. 

How to enable product attribute below product item?

This feature only applies to variable products.  Go to Theme Settings > Shop Settings > Shop Catalog > Product Attribute to select the attribute you want to show on.

You can change the attribute for a product you want. Edit a variable product > Product Attribute tab and select the attribute you want to show.

How to show attribute swatches widget on sidebar?

Go to the Appearance -> Widgets section and add Woodstock Attributes Filter widget

How to show the selected attribute's label?

Navigate to Appearance -> Customizer -> WooCommerce -> Variation Swatches and check "Show the selected attribute's label"