appreciate all your answers, thank you!

You're right, 100$ is not much to expect some serious wins but to get a sense of what's going on it's fine.
For a newbie (like me) it is really difficult to understand the whole cryptocoin market. Of course, "everyone" knows Bitcoin and probably Ether and Litecoin but if you try to find some information about other coins (like Monero) you will fail (or at least I failed). It's like ask someone and (s)he will recommend something else.

Whatever, I bought some LTC and Ripple for my bucks and just watch the market the next couple of weeks / months.

If I can make some profit --> great (and maybe I am going to invest a larger amount than just 100$)
If I loose the bucks --> who cares (at least I tried)