Jisho

• Tae Kim's Guide to Learning Japanese: Performing an action on a subordinate clause （と、って）
• IMABI: The Particle と II: Citation, The Particle と III: と + …～ない, The Particles って, たって, & だって

The word だ, and its polite form です, is similar to the English word “is”. Here are a few good articles to learn more.

• Tae Kim's Guide to Learning Japanese: Expressing state-of-being, Formal Expressions　（である、ではない）
• IMABI: Copular Sentences I, Copular Sentences II, Copula Verb Variants