What should I invest in?

I finally have a decent paying job again where I have some extra money to put into stocks and I don’t know where to begin.

I am investing in a 401k and a Roth currently but want a portfolio separate from those.

I keep getting and offer from Webull saying if I deposit $50, I’ll get $100 worth of fractional shares of TSLA. Is that good? What are fractional shares? Where should I begin? A lot of questions lol but thanks in advanced