You are looking for platforms that provide with data. The most popular crypto web-sites are coinmarketcap and coingecko. Personally I prefet using CoinMarketCap. You can check prices, market cap, total supply, daily trading volume etc there. What is more, there is a good table of top-100 coins which I use to find new altcoins to my portfolio. Also you should subscribe to some channels with news so as to follow this market (Forklog).