Early modern English is a name for the modern English language the way it was used between around 1485 and 1650. Thus, the first edition of the King James Bible and works of William Shakespeare are both in early modern English (though the King James Bible intentionally keeps some anachronisms that were not common even when it was written). Current speakers of English are generally able to understand early modern English, though occasionally with small difficulties due to grammar changes, changes in the meanings of some words, and spelling differences.
Early modern English, as with most European languages, had T-V distinction. That is, there were two versions of the second person pronoun: "ye" (plural and formal singular, superceded by the accusative "you") and "Thou" (accusative or casus generalis "thee", from Indo-European "te"), (informal singular). It became customary to address God in the "thou" form, and when thou was abandoned by most English speakers, its continued usage to address God caused Late Modern English speakers to mistake it for a formal pronoun. Verb conjugations in the "thou" form end in -(e)st. In Early Modern English, third person conjugations end in -(e)th instead of -s. Both the second person informal singular and third person singular lost their endings in the subjunctive, which utilizes the bare stem of the verb.
See Modern English for more information on English as it used from 1650-present.