understanding OpenGL

OpenGL is a cross-platform API to graphics hardware.Each procedure must be invoked within a current context.The context is created,shared,made current and destroyed in a platform-dependent manner.The API can be used to specify various objects and context states.The objects include buffers,shaders,programs,program pipelines,textures,samplers,renderbuffers,vertex arrays,transform feedbacks,queries,fences.The interaction among objects and states is defined in a pipeline.As a model,the pipeline is not exposed explicitly.The pipeline consists of  programmable stages and state-driven fixed-function stages.A shader operates on a single type of data,either vertexes or fragments.A vertex is a collection of ordered attributes,each attribute is a scalar,vector or matrix,with assigned semantics.