The four noble truths are by legend the first teachings of the Buddha after his awakening. They are:
1. Experience is marked by dukkha (varyingly translated as suffering, dissatisfaction, etc.)
2. The cause/origination of dukkha is desire, anger, and ignorance (meaning: ignorance of our true nature)
3. There is a way to end dukkha.
4. This way is the eightfold path.
You can’t ignore the four noble truths; they are the heart of all Buddhisms. But the Mahayana does not simply take them at face value. In its explication of emptiness, the Heart Sutra negates the first three — “no suffering, no origination, no stopping…” And Zen teachers generally emphasize practice, instead of the eightfold path.
For more information, see https://en.wikipedia.org/wiki/Four_Noble_Truths