You can begin by initially training the agent. You can train MARA using the ppo2_mlp.py script, as follows:
$ cd ~/ros2learn/experiments/examples/MARA
$ python3 train_ppo2_mlp.py
You can try out the -h argument to get all the available commands for this script.
Now that the robot arm has been trained, you can test the trained policy using the following commands:
$ cd ~/ros2learn/experiments/examples/MARA
$ python3 run_ppo2_mlp.py -g -r -v 0.3