How to start investing in bitcoin?

Hello. I have a question. I just got interested in cryptocurrencies and would like to invest part of my wallet in bitcoin. How to start investing in cryptocurrencies? Could you recommend a place where I can easily and, most importantly, safely buy my bitcoin and then sell it without any problems? I would like to add that I am interested in purchasing with a debit card. Is there such a possibility at all?

Another question is the storage wallet. I would like to ensure maximum security of my bitcoin, but I am curious if it is worth buying a ledger or trezor hardware wallet as a beginner? Perhaps they are intended only for more advanced cryptocurrency users? What do you think, is it better to buy or rely on wallets that I can install on my smartphone? Thank you very much for all the advice and suggestions. Regards, David.