How can I be a better manager?

I have be recently hired as a Head Cashier at one of the biggest home improvement warehouses. I am over at least 30 people. I am not good with confrontation and have been told I'm "too sweet". What would be the best way to approach people who are doing something they shouldn't be, like texting or mot being where they are supposed to be. What are your stories, experiences, and how did you handle the situation? Any tips? Thank you in advance!