Beginner on 212 with £30k to invest. Advice pleassseee

I am not sure what to do. Whether to put some of this sum in an ISA on trading 212 then the rest invested in different stocks and shares. I’ve heard go with FTSE 100, S&P 500 etc etc. obviously I’d like to spread it over quite a few companies. Can anyone make it simple for me to begin with as I’m feeling so overwhelmed with the options on that app and where I should put my money. I don’t want to copy anyone’s pie either I’d rather do research and make my own but would like people’s opinions/advice also.