Here is a link to some educational material from an organization that I invest through. This organization handles investments for Public Sector employees, but the literature will still be helpful.
I encourage you to read as much as possible! There is so much to learn! Stocks - large cap, small or mid cap? Growth or Value? International? Diversifying - holding not just different funds, but making sure they are invested in different sectors of the economy (tech/healthcare/retail). Learning about the funds - past performance, have they changed managers, etc? Expenses!!!
I have invested in mutual funds for many years. In a mutual fund, the fund manager is supposed to stay knowledgeable and invest the funds assets in various things. This is because I don't have time to figure out how the rumored proposed trade tariffs will affect my funds and what I should do!
When you are younger, you are supposed to take more risks, as you have more time to recover. (invest mostly in stocks, not bonds.) But it is not easy to take risk and not interfere with your own plan. For example, losing 10% of $1000 might be okay, but how will you feel about losing 10% of $10,000? It's the same loss, but more money!
One thing I will say is this: if you have an employer who offers a 401 match, if you contribute x% of your income, take full advantage of it!
Anyway, here is the link. Good luck!