Infants progress from supporting themselves on their forearms and creeping on their tummies, then move into the crawling position and learn to crawl on different surfaces, up slopes and steps and over obstacles.
Most infants will happily lie on their tummies and quickly learn to push on their arms, lift up their heads and view the works from a different vantage point. Many infants on the other hand hate being on their tummies on a horizontal surface and may need quite a bit of encouragement to get them happy in this position.
I often see infants aged between 11-15 months who have learned to sit but are not rolling, hate being on the tummy and are not crawling. Parents are understandably getting anxious about their infants development and may have been advised to work on tummy time.
Infants who dislike tummy time will often be quite happy when positioned on their tummies at a low block. In this position it is easier to push up on the arms, look ahead and to start reaching for toys with one hand.