There are tons of exchanges from where you can send you're btc or ethereum and buy alt coins from I will give a few exchanges from which you can easily make the transactions. Some exchanges take longer to verify but are safer like bitterex coin exchange.
One of my favourite exchanges is binance, you can make your account from the link below.
https://www.binance.com/?ref=13958879
there are other exchanges too like yobit
https://yobit.io/?bonus=xrNrr
My favorite exchange to use is called Bitshares. https://bitshares.org/
I personally prefer binance but cobinhood looks good because its decentralised
Good post