If you want to start trading, start with local bitcoins (localbitcoins.com) and hopefully you can find someone in your area that you can sell bitcoins to. Do small amounts first. Also, learn about the buyer's side by buying small amounts first.
If there is nobody local, then find a reputable online buyer/seller and buy/sell via cash-deposit to a bank. It is the least risky.
Once you get a handle on local trades, I would then consider joining an exchange. There are so many to choose from, and it depends if you are from the U.S. or from Europe. I know people who have had luck with Gemini, Circle, and itbit. For Europe: bitstamp and btc-e seem to be the best.
But take it slowly. It can be rough out there and there are scammers around every corner.
Good luck!
but i think trading on localbitcoins is harder for someone who wants to start trading because first of all you will need reputation to be able to trade more and also the worst part is the scams that can happen while using their services.
Nah, with that logic, nobody would start trading! You have to start somewhere, right?
Especially for those who are new to trading in general, I would start with a local person-person trade. It takes the least amount of risk, $, and know how. You don't have to know anything technical, and if you have any sense of customer service skills, you may get a repeat customer.
What local buyers are looking for are a reasonable price, convenience and someone who won't scam them. If you agree to a public place like a fast food place, etc., that will reduce the worry in the buyer. If you send directly to a wallet, follow the confirmations on blockchain.info. Wait for at least 1 confirmation.
What will win you business is price, customer service and common sense.