puts are for options. and that is not done in most of Europe (as its not popular), besides apparently 2 specific places.
What Trading212 offers are CFDs in which you buy long or sell short against a stock or commodity.
If you want my honest advice, do not attempt to try this with the current market while being new to the concepts you are learning about, you will only harm yourself irreversibly for no reason. Instead, spend the next week or 2 learning about CFD trading, while practising on the practice CFD account with virtual money.