If you want to buy altcoin then you must have BITCOIN or ETH first and you can buy altcoins on the stock such as bittrex or others. There are various lists depending on the country of residence you are in. we see in the State of Japan or America are two countries with lots of trading floor, which is unlikely you do not know of both countries. For trading coins, you should search on various web trading or on youtube which is discussed by many people.