1. A term to motivate an individual or group of people to get on with a task in hand, especially after being demonstrated or explained the task first. Similar to get a move on.
2. Understand or see. By not inderstanding what someone meant verbally, or not seeing something so not knowing what was happening. Usuallly not seeing or under something that was meant as a joke. Similar to catch on.
1. 'hurry up and crack on with it'. Or 'get cracking'
2. 'did she see?' 'no she didn't crack on to what you were doing'