How can I activate the Offers Page (Bundles page)?

When you install the app and start creating bundle offers, we will create the Offers (Bundles) page for you automatically.

Its link is probably: {your website address}/pages/bundles

If you want to add the page to the main menu of your shop, you should go to the navigation panel in your Shopify's admin panel and add it to the menu like the other pages.