How should i start my investment portfolio as a fresh graduate

I just started work in a government ministry (so should be stable income) and i want to start investing. what is a good platform to start, and a way of investing where i dont have to buy and sell stocks (im quite new all i know is i should buy s&p but i dont know what that means or how to do it), so basically a passive kind of investing is good (one i can just put in some money every month to grow)