There are two most important points about TensorFlow.

### Basic elements of TensorFlow program
Tensorflow program represent the compuation using data flow graph, which includes the main four concepts:
- graph
- session
- tensor
- operation

## Phases of TensorFlow program
The TensorFlow program can be divided into two phase:
- Phase 1: assemble a graph
- Phase 2: use a session to execute operations in the graph

It's important to be aware of which phase you are in. It can help you not only to do the right thing in different phase but also to understand the problem in tensroflow program.
