Can I just use it without a card by adding cash

You can add cash to the Apple Cash card. That is card you can use with Apple Pay. click here ➡️ Set up Apple Cash - Apple Support

Outside of that, no. Apple Pay uses debit or credit cards. Not direct cash balance.

You can use most Visa or MC reloadable or pre-paid debit cards if you wish. That way you only add what you want to spend to that particular card.