System design basic query- DBMS

Hi, I'm aiming to learn system design. I know coding and DSA but i heard that we need DBMS for system design. I've no experience with a DBMS, I'm looking to learn but hesitant on what to begin with – there is SQL, no SQL, my SQL… I even don't understand what they differ on and what shall I begin with. Can someone guide, I'm a total newbie in this DBMS and planning to strengthen it from basics. Tutorial links and all/books recommendation alongside will help.