Most babies begin to crawl when they turn 6 months of age.
However some babies may not be ready to crawl until they are 9 or even 10 months of age.
I've known a few babies that never crawled and just started walking and standing up on their own.
So it's not a problem if your baby never crawls however most babies do crawl first before they stand and walk.
When a baby is ready to stand and walk they will begin pulling themselves up on things such as the couch, coffee table etc.
When a baby is between 9 months to 12 months of age the baby will usually be ready to start pulling themselves up to standing position on things.
Sometimes babies do it even by age 8 months and are ready to begin walking.