How to resolve my canonical issue?

Hi Guys i was facing “Page is not indexed: Alternate page with proper canonical tag” please anyone tell me how to fix it
my website

Your site has the same content on multiple pages, and lacks the proper <link> tag for the search engine to determine which is the one master copy that should be indexed.

How to Specify a Canonical with rel=“canonical” and Other Methods | Google Search Central | Documentation | Google for Developers

thank you for your advice but the problem is i was completely new to SEO so it was very difficulty to understand each and every one