Just starting out...what are the best, safe exchanges to buy/sell bitcoin, ethereum if you’re in the US. What about trading for alt coin?
Using Coinbase no doubt is "one" of the easiest way to buy bitcoin in US if you meant to buy it via fiat. Although you must understand and learn first their fees if it's reasonable to you. You can also sell bitcoin here but you are dealing with the company itself and not on the usual trading platfrom where you are trading with the trader itself.
For trading (we are talking about buy/sell bitcoin in US), you can try Bitstamp, Bitfinex, Gemini. These are large exchanges and operates for long time now although as usual there is downsides like fees, methods and Bitstamp & Bitfinex have a hacking history.
For the usual trades, you can try Poloniex, Bittrex, Crytopia, HitBTC.
Remember that best and safe exchanges will depend on your experience. You will get random responses here but the final view about that exchange will depend on you.