If you choose to keep some stored on an exchange or a website such as Coinbase, then ensure you complete a full security setup and ALWAYS setup Two Factor Authentication, I recommend using Google Authenticator for this and not SMS Two Factor Authentication as your phone can be compromised by hackers. Google Authenticator creates a random number string each time you log in to protect yourself in case someone can get hold of your username and password.
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.
Always pay attention to Bitcoin. Most altcoins (every cryptocurrency except Bitcoin) are pegged more closely to Bitcoin than Asian currencies were to the USD during the Asian Financial Crisis. If Bitcoin price pump drastically, altcoins price can go down as people try to exit altcoins to ride the BTC profits; inversely, if Bitcoin prices dump drastically, altcoin prices can go down, too, as people exit altcoins to exchange back into fiat. The best times for altcoin growth appear when Bitcoin shows organic growth or decline, or remains stagnant in price.