Buddha's teachings are many and diverse. They comprise 84,000 teachings, he has given over 45 years. Traditionally, the teachings are divided into three "collections" or "baskets", which from a Western point of view can also be seen as three pillars of a building, i.e. vertically. Each pillar itself consists of three parts, therefore Buddha's statements can be summarized in nine basic groups altogether.
The first pillar is the required knowledge of Buddhism. If questions arise, the answers can be found here. But for a Buddhist it is not enough to know. Therefore the second pillar accords to translating knowledge into experience. This is achieved by means of various meditations. To stabilize experience, eventually, Buddha adds a third pillar, where he explains, how to permanently substantiate knowledge and experience gained from meditation.

When looking at the teachings from a different perspective, you can also divide them horizontally into three levels:
The first level attracts people, who mainly have their own development in mind, who wish to leave the cycle of suffering as fast as possible. Regarding the single pillars in the sequence given above, Buddha mostly explains cause and effect (Karma) to these people, so they can consciously build up causes for happiness and avoid those for suffering.
 Understanding that positive actions lead to happiness and negative ones bring difficulties, one can fully take responsibility for one's own life. Therefore, meditation is structured in a way, that one can learn to deliberately decide in every situation, how to feel, think and act in order to accumulate good karma. Mind is calmed and from the space gained by this arises freedom. In order to keep this experience, one develops awareness to stop following bad habits. Often this is done with the help of outer vows. Therefore, many monks and nuns can be met on this level.

The second level addresses altruists, people who have surplus energy for others and who care more for others' well-being than for their own. Here first, you have to develop an understanding that you need a well proportioned blend of two things: on one hand there is compassion, the understanding that other people are caught in the cycle of existence as well, and that they do not act out of malice but ignorance. On the other hand, one also needs intuitive wisdom to give others what they need for their development. Meditations concentrating on these points include all beings. Moreover you start to develop an understanding of or feeling for the space-like nature or emptiness of all things.
Emptiness means, that nothing has a permanent nature of its own, but everything is composite, changes constantly and will fall apart sometime. To keep the level one has reached through meditation, most of all, you learn to avoid anger, and to experience pleasant impressions as blessings, and difficulties as a process of learning and purification.

The third level addresses realizers (or "Yogis" as they were called). These are people, who have a surplus for others, who constantly identify with the goal of enlightenment and who, because of their insight, can  hold opinions, which do not always conform to what is regarded as politically correct. On this level, you recognize that Buddha is the mirror of your own mind and that all people possess Buddha nature. Nothing has to be added from the outside. The structure of all meditations completely aims at merging with enlightenment. Here, you either work with meditation aspects, which symbolize the different qualities of enlightenment, or with mind's own awareness. This level is best kept with the help of the "pure view": A joyful level of experience in every situation, towards all people including oneself, takes you closer to absolute truth. Mind's clear light is experienced as rich and playful.

This is a Buddha's view, beyond all conditions. Here, everything is fantastic for the very reason it can happen.
The roof of the building are Buddha's teachings on the most powerful meditations, which aim directly at the nature of mind. They are called "the Great Seal" (Skr. Mahamudra).  Here, one practices the union of basis, way, and goal – beyond expectations, hopes, fears, beyond yesterday, today and tomorrow.