Tensorboard shows the graph of the network you are using. It is usefull to debug the definition of the nodes you are using. First the graph must be written in a file and then it can be rendered as a image.
Once the graph is defined and the session initialized, the graph is exported with:
writer = tf.summary.FileWriter("output", sess.graph)
sess is the session object and
"output" is the output folder where the definition will be stored.
Once the definition is stored in a file, the graph can be rendered with the command:
python -m tensorboard.main --logdir="[path to the folder with the graph definition]"
This command runs a web server and using the web browser can be seen the generated graph.