There are several ways of generating income either free or as a type of interest from cryptocurrency. Below I have listed a few:
(1) Airdrops - these are projects that give free cryptocurrency in exchange for you performing some task namely:
(1.1) XLM Stellar Lumens gave airdrop if you download an app called keybase which is like Whatsapp but has an integrated crypto wallet where you can store XLM . Similarly Energi project gave 100 NRG for completing KYC and some social media tasks.
(1.2) Coinbase give a little bit of several partner cryptos for downloading ttheir app and watching a few videos about those crypto projects and answering a couple of multi choice questions.
(1.3) A crypto wallet called Blockchain has partnered with a couple of projects and given $10 of XLM and currently $10 of Blockstack if you download their wallet and perform KYC.
(2) Many crypto projects allow you to stake their coins in return for more of their coins or a dividend coin e.g NEO & GAS , ONT & ONG, WAN &WAN , ICX & ICX, NRG & NRG etc
(3) You can now get a small amount of crypto for internet browsing using the Brave browser which you will need to download. You get BAT tokens for allowing adverts to be displayed. You can withdraw these to a wallet they sponsor called Uphold and from there withdraw to wherever you wish.
(4) There is another website called Publish0x which allows you to post blogs and articles that people can tip in crypto.
There are many other ways to earn crypto which I probably am not aware of but if you want to enter crypto without spending any money the above avenues are just some of the ways you can do that.