Both liquid water at 100ºC and steam at 100ºC consist of water molecules, however, the particles in liquid water are closely packed and have less energy compared to the particles in steam, which have higher energy and are spread out.
The similarity is that both liquid water and steam at 100ºC are composed of water molecules. The difference is that in liquid water, the molecules are close together and constantly moving, while in steam, the molecules are more spread apart and move more freely.
