Co-signer situation: what does my dad actually agree to if he co-signs my lease?

I'm a first-year teacher, income is $38,000/year, and I don't meet the standard 3x rent requirement for the apartment I want. The landlord says a co-signer would work. Before I ask my dad, I want to understand: is he just guaranteeing that I pay, or is he actually on the hook for the full lease if something happens? NC specific answers welcome.