python return.py to compute return. You need to have downloaded the balance_history.csv using Export history button under balance (full history!). To see how I computed the return open return_math.md.
python rebalance.py will tell you how many stocks to buy (positive) and sell (negative) for each position according to the portfolio you define on the same script.
I assume that you have credentials/credentials.json and credentials/client_id.py. I added some examples, but note that credentials.json gets modified so you shouldn't expect to have the same format.