What are the differences between sound waves and electromagnetic waves?

Propagation:
Sound waves are longitudinal, meaning that the vibrations occur parallel to the direction of propagation (travel).

Electromagnetic waves are transverse, meaning that the vibrations occur perpendicular to the direction of propagation.

Medium:
Sound waves are physical, so the oscillations are formed from vibrating solid liquid or gas, so require a medium to travel through.

Electromagnetic waves cause oscillations in electric and magnetic fields, so do not require a medium.

Speed:
Sound waves travel at about 300 m/s (but is dependent on the medium).

Electromagnetic waves travel at the speed of light, i.e. around 300,000,000 m/s.