First, what is the best exchange? The best exchange to use is a tough question, their are many that have benefits and negatives.
You can start at Coinbase it is very easy to use, and the transactions fees are not to high. Eventually you can get gdax which is apart of Coinbase and you can store usd to purchase crypto right away.
Start with Coinbase now
==> https://www.coinbase.com/join/574fbd5f2a867d019b0010a6
Another good exchange to use is coinmama. Coinmama you are able to use your credit card. Coinmama never stores your crypto it sends it directly to your private key(wallet)
Try it out, see if you like it
==> https://www.coinmama.com/?ref=addev23
Other exchanges you can try: bitfinex , kraken, jaxx, and Bittrex.
Now the most important thing is trying to find the best way to keep all your crypto safe. What I did is I created my own wallet from blockchain.info. It is very easy to create and when you create the wallet make sure you use google authy for the two-step verification .
This wallet will be able to store your bitcoin and ethereum.
Another place you can go to create your own wallet is a place called BitGo. With BitGo you can store your bitcoin securely, your litecoin securely and even bitcoin cash securely.
Once you can get these simple steps down your on the right path to becoming your own bank!!!!