A portfolio contains more information than a watchlist. Portfolios are designed to track the stocks you actually (or hypothetically) own. Portfolios maintain a list of the individual investments (stocks, ETFs, mutual funds), and, for each investment, the number of shares and the average purchase price for the shares. Stock Rover uses that information to calculate detailed performance data for the portfolio.
A watchlist is similar to portfolio, but only contains a list of tickers—no quantity or buy price information is entered. A watchlist is generally used to track securities that you are interested in but don’t own.