The idea of karma expressed in the commonly known phrase "actions have consequences" is captured in the Pali word pair kamma-vipaka, which is to be understood as referring to intentional actions, and results (consequences) relating to states of being and (re)birth of the actor. In the Lam Rim tradition¹, karma is understood to have four characteristics:

1. Karma is definite: Unskillful actions (akusala-kamma) lead to dukkha (stress, suffering, pain, distress, discontent) and skillful actions (kusala-kamma) lead to sukha (pleasure, ease, satisfaction).
2. Karma is fast-growing: It is said that its strength doubles overnight, particularly if the action (skillful or unskillful) was accomplished by strong intention, fully carried through, with satisfaction at its accomplishment.
3. If you create the cause through skillful or unskillful action, you will definitely enjoy or suffer its ultimate effect respectively, with a couple of exceptions:
   • In his Guide to the Bodhisattva's way of Life, Shantideva says:
     Whatever wholesome deeds,
     Such as venerating the Buddhas, and generosity,
     That have been amassed over a thousand aeons
     Will all be destroyed in one moment of anger.
     -- Bodhisattvacharyavatara , VI.1
   • In the performance of an unskillful action, you plant a seed of future suffering. However, through appropriate practice of repentance and purification, it may be possible to prevent the conditions from arising under which that seed can grow and bear fruit.
4. If you do not create the cause, you will not experience a resulting effect.

¹The earliest appearance of this four-point formulation that I can find is in Volume 1 of Tsongkhapa's Great Treatise on the Stages of the Path to Enlightenment, which was completed in 1402 AD.