There are various way were one can earn free Bitcoins-
By Mining
You can earn Bitcoin by mining them, but first the mining rewards have reduced significantly.
The cost of setting up a Bitcion mining farm is too much, you need to invest in crores to set up hardware machines which can mine bitcoin.
By referral program
Well you can earn free BTC, if you know a bit of affiliate marketing, there is a very simple Referral program which CoinSwitch exchange offer.
Refer your friends and earn $5 when they complete a transaction for a minimum of $100. And guess what?? Your friend earns $5 too. Isn’t that awesome!!
