Some of the fundamentals of the teachings attributed to Gautama Buddha are:
The Four Noble Truths: that suffering is an ingrained part of existence; that the origin of suffering is craving for sensuality, acquisition of identity, and annihilation; that suffering can be ended; and that following the Noble Eightfold Path is the means to accomplish this;
The Noble Eightfold Path: right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, and right concentration;
Dependent origination: the mind creates suffering as a natural product of a complex process;
Rejection of the infallibility of accepted scripture: Teachings should not be accepted unless they are borne out by our experience and are praised by the wise. See the Kalama Sutta for details;
Anicca (Sanskrit: anitya): That all things that come to be have an end;
Dukkha (Sanskrit: duḥkha): That nothing which comes to be is ultimately satisfying;
Anattā (Sanskrit: anātman): That nothing in the realm of experience can really be said to be "I" or "mine";
Nibbāna (Sanskrit: Nirvāna): It is possible for sentient beings to realize a dimension of awareness which is totally unconstructed and peaceful, and end all suffering due to the mind's interaction with the conditioned world.