Where you stand

I just started earning and have nothing invested

If that is you, here is what this situation usually involves, in the order it usually comes up: the things worth checking, what each one is, and where the arithmetic for it lives. None of it says what to do.

1. A cash cushion is one to three months of expenses kept somewhere plain and reachable; what one month of your own bills comes to is the first number worth knowing.
2. Whether your employer matches retirement contributions, and the formula: a match is money the employer offers only on the part of pay that is contributed, and what is not contributed up to the match is offered and kept.
3. Whether your health plan is a high deductible plan, which is what opens a health savings account, the one account that skips tax on the way in, while it grows, and on the way out for medical costs.
4. A Roth IRA is open to anyone under its income limit; the arithmetic turns on one number, your tax rate now against your tax rate when the money comes out, and at a low rate now the tax paid today is a known small figure.
5. What a broad index fund holds, what it costs each year, and how that compares with the fund's alternatives, which is the comparison the fee calculator prints in dollars.
6. Options, crypto, and single stocks are where money that was needed later most often disappears; the guides below show the arithmetic of each before any of it is real.

Read these

An account is not an investment
Workplace plans: the 401(k), the 403(b), and the TSP, from the first paycheck to the last
The health savings account: three tax breaks and one gate
Roth or traditional: two jars, one tax bill
Funds: what you actually own when you buy one
What a one percent fee costs over a working life