To remove a ticker - right-click the ticker and select "remove XYZ from this watchlist." You can also select a range of tickers and remove the selection.
You can add or removes columns using the columns button on the right-hand side of the tool.
The notes feature allows you to enter custom notes about a stock. You can also use this as a trading journal!
You can set alerts for each individual watchlist by clicking on the bell icon at the top of the tool.