Ask HN: What are your best and safest investment options?

I'm currently in my early 20s and since getting a job as a software engineer, I started to save up more and more. For all the money not to go to waste and just sit in the bank account, I would like to start investing, and slowly add to it every month. What options do I have? I'm based in Europe if that matters. I also perfectly understand that safe means lower return and I'm perfectly fine with that, since I am going into this for a long term.

Also, any useful resources regarding investment would be helpful (YouTube channels, books, etc.).

Thank you!