This setting enables you to add a dynamic title to your online store.
To access the Dynamic title settings, click Customize (Themes section on Shopify) > click on Theme settings > Dynamic title
On page titles
Titles to rotate when customer is on the page. If left blank, it will not be used.

Left page titles
Titles to rotate when customer is not actively on the page. If left blank, it will not be used.

Rotation interval
This setting will change the times it takes for the title to rotate.