If everything is new, maybe you can start with:
- the official website: https://bitcoin.org
- Bitcoin wiki pages: https://en.bitcoin.it
- The free version of "Mastering Bitcoin" book: https://github.com/bitcoinbook/bitcoinbook

Edit: The main/"official" Bitcoin wallet is called Bitcoin Core. There are also altcoins (forks of Bitcoin) with the word "Bitcoin" in their name, some of them (especially Bitcoin Cash and their website bitcoin[dot]com) even attempting to claim (false advertising!) that they are the true Bitcoin and so on.
Some started calling the first coin Bitcoin Core exactly to avoid misunderstandings and get confused with those altcoins.