The answer is:
"I love it," She said loudly.
"Yep," I said. "I knew you would."
You need quotation marks when someone is speaking, when they start and when they end. When the quotation mark ends if the punctuation is supposed to be a period (does not apply for ! or ?) you put a comma instead. You also start a new paragraph every time a new person speaks.
Hope this helped!
