Croatia is known as a safe place for visitors. People are free to move anywhere they want during the day, and in most places during the night. Especially, you can feel the relaxed atmosphere in coastal destinations like Split or Hvar.
That being said, you still need to take basic precautions while travelling in or around Croatia.
It means taking care of personal stuff in the first place. I recommend keeping your bag visible in front of you while walking. When going to a beach, you should take only a minimal amount of money necessary for a cocktail or a coffee.
Respect nature! When visiting natural attractions like Plitvice Lakes or Krka National Park, wear suitable footwear and follow the weather forecast. Do not drink alcohol before visiting such places. Although accidents are rare and safety is at a high level, it is important to be prepared and focused.
The only official currency in Croatia is euro. Most of the shops accept it as the only way of payment, and only a few accept dollars or pounds. Additionally, most of the shops accept credit/debit cards as a way of payment.
I recommend having some euros in your wallet all the time. You can exchange it for other currencies in banks or exchange offices.