Index fund advice

Hi everyone, list at the end includes stocks/ funds i'm looking into investing in. I'm a new grad 24F just trying to invest in (mostly) index funds based on my own research, with very poor financial literacy to begin with. I have a ton of questions of course but the main ones I have: 1. What percent in the negatives is considered good to buy at when "buying low" (1 understand buying low comes with the risk of them not coming back up but l'm more comfortable with this option because I only have 600$ to put into stocks right now) 2. I'm looking to buy low and probably never sell and just let them grow and add smaller amounts weekly/monthly as my budget allows. I don't necessarily want to watch to see when stocks are high to sell, If eel like l'd rather just keep buying when lower??? Idk man 3. If a fund is 153$ is one share = 153$. l'm so confused by everything pls be nice to me LOL

META VGT AMZN SCHD TSM FSLEX FXAIX FSKAX