The first step in buying altcoin is to create a wallet first.  MEW (Myetherwallet) is one of the most popular wallet because it is ERC20 compatible.  Once your wallet is set up then you can buy in exchanges like Etherdelta, Yobit, Cryptopia ...you can also buy in token sale of ICO's.  Do not forget to prepare your national issued ID because you have to fill up a KYC form.  Make sure that your country is not listed in the list of banned countries.  Sometimes buying in ICO is better than exchanges because they provide bonuses for your purchase.  Remember that investment is always a risk.  Always do a background check on the altcoin that you are going to buy but intuition can also help in finding a good buy.