What is the difference between steric and torsional strain?

#color(red)("Steric strain")# is resulting from the fact that bulky substituents occupy large space around a carbon atom which will result in getting the substituents closer to each other, and therefore, their electrons will be repelling.

#color(red)("Torsional strain")# is resulting from the repulsion of the electrons forming the bonds of two adjacent carbon atoms. We talk about torsional strain mainly when we draw Newman projection in the case of Eclipsed and Staggered.

Steric strain is higher in the case of eclipsed conformation because the bonds are in the closest position to each other, however, it is the least in the case of staggered since the bonds are the furthest apart.

Images source: Organic Chemistry-Janice Gorzynski Smith 3rd Ed

Here are videos that explain Newman projection and their energies based on the type of strain exists: