What does "我牛起来" mean? I know what each of the characters mean, but I'm confuse on how to put it into a sentence.
我 - I
牛 - ox
起来 - up
“我牛起来” means “I’m gonna be better/successful/cool”
In this sentence, “牛” is short  for “牛逼” which is meaning of  “super cool”.
Why does “牛逼” mean “super cool”? You could find the answer in this video
https://youtu.be/teQPusK7YFU