ICOs, as you may have guessed, are much like IPOs. This is where coins are offered for the first time to the public. ICOs are not offered through exchanges, but rather you buy them directly from the creators of the project. Usually (it’s different for each project) you will send them Bitcoin or Ethereum that they will use to fund their project; in turn you receive a certain amount of their new coin.
For people who don't pay attention to development trends - one observation of high significance is Go popping up in the popularity list associated with Ethereum. Why is Go in particular an important sign? It's almost as fast and less clumsy compared to C++ and C Sharp. At the same time, it's relatively new. People who know Go are experienced and choosing to learn it because it is better. In my opinion, it will be the default backend language for most Silicon Valley tech companies in the next 5 years. Those same people are choosing to play around with Ethereum using Go.
Poloniex was started in the year 2014 and has become a preferred platform for crypto exchange and trading since then. You might want to pay attention to this US based platform as it offers more than a hundred cryptocurrencies to its users for trading. What makes the exchange unique probably the most preferred choice of people like you is that, it holds the highest volume for Ether as it supports both Ethereum and BTC markets independently.
To perform cryptocurrency arbitrage, you need to find an opportunity where you can buy a cryptocurrency for less than you can sell it on another exchange (minus the fees and commission). Once you’ve found one, all you need to do is simultaneously buy Bitcoin on the lower-priced exchange and sell on the higher-priced one. It’s easy to make hundreds or even thousands of dollars in just a few seconds if you have enough funds.
When buying coins, and especially with Bitcoin, you will notice that your purchase is in decimal. A Bitcoin itself is relatively expensive, around $10,000 at the moment (as of 15th Feb '18). If you were to purchase say $5,000 of Bitcoin, you would at today's rate be purchasing around 0.5 of Bitcoin. Do not ever worry about this; Bitcoin operates at eight decimals places. You do not need to own a whole Bitcoin or any coin for that matter. Consider it like pence in the pound or cents in the dollar, but with more decimal places.