Tip: 以上 basically means “this or more/above”. For example りんごが3つ以上ほしい means “I need three or more apples”.
以上です is closer to EOM (end of message) in English. In a letter/email, you state what you want to say. And then, you end your message with “EOM”.
In Japanese, we sometimes end it with 以上です, meaning “the abovementioned words are all what I wanted to say.”
You can use the phrase 以上です also in a dialogue.