What is the difference between sunna salat and nafl?

Bismillah hir rahman nir raheem

Sunnah Salat are themselves Nafls that our Holy Prophet (S.A.W) prayed and this is why they are called Sunnah Salaat.

There are two types of Sunnah Salaat.

1. Sunnat-e-Muaqqadah
2. Sunnaht-e-Ghair-e-Muaqqadah

Sunnat-e-Muaqqadah are those sunnah salaat which our Holy Prophet (S.A.W) prayed regularly before and after Fard (Obligatory) Salaat respectively.

Sunnaht-e-Ghair-e-Muaqqadah are those sunnah salaat which our Holy Prophet (S.A.W) prayed but not every time.

Sunnah Salaat have greater reward then Nafls.

And yes, you have to make intention (Niyyah) for Sunnah Salaat before you perform them.

However, Nafls are not limited, you can offer as many nafls as you want but their reward is lesser then Sunnah Salaat.

Hope you are clear now :-)

The niyah must be in the heart and it should not be mentioned as we all know that ALLAH is ALL KNOWING so our sunni shikhs told us that, performing the wodho is a sign that we are going to pray so intention is seen :) and ALLAH know more.