You might enjoy this article about ICO
https://themerkle.com/cryptocurrency-ico-education-the-basics/ .
Basically, an ICO is a Kickstarter or fundraiser and their is no guarantee on any kind of gains, which creates a risk for the investor. As an investor, you will be given tokens almost like shares I think of it, but the value of the tokens could be nothing.
Alt currency, I think you are talking about crytpocurrency? Depending on what kind of crypto you purchase, they have different functions, but they ultimately have some kind of cash value and are easier to liquidate then an ICO. The safer investment would be the cryptocurrency since they normally contain a tradeable value.
