Learn Turkish: Yarın bayram, okul kapalı. - Tomorrow is a holiday; the school is closed.

In Turkish, you often don't need a verb for "to be" (am/is/are) in the present tense when stating basic facts. Yarın bayram simply means "Tomorrow is a holiday" and okul kapalı means "the school is closed."

Where are the words for "a" in "a holiday" and "the" in "the school"?

Turkish doesn't have a specific word for "the", so okul naturally translates to "the school" based on context. For "a holiday", you could use bir (one/a) and say bir bayram, but it's completely normal to leave it out when just stating what kind of day tomorrow is.

Since we are learning about months, how would I add "in May" to this sentence?

You would use the month Mayıs and add the locative suffix -ta (meaning "in", "on", or "at"). Because months are proper nouns, you separate the suffix with an apostrophe: Yarın Mayıs'ta bayram, okul kapalı.

What is the difference between bayram and tatil?

Bayram specifically means a national or religious festival or public holiday. If the school were just closed for a regular weekend, a normal school break, or if you were taking a personal vacation, you would use the word tatil instead.