Without certain knowledge, it is better not to invest. But if you are a beginner and still want to buy some kind of coin, then start with bitcoin or Ethereum. This will be the most reasonable and reliable solution.
Starting as a newbie by investing in bitcoin or ethereum is a good choice. If you want to try, you may invest a bit, then feel the trading. Is it good? If it's yes, you can invest your 750$. But if it isn't, you may choose to leave or stay and learn bit by bit again.