The input field for selecting a station is an auto-suggest input field. You can select
stations by first selecting a network in the "Select network" pull-down and then
typing some or all of a station id or station name in the "Enter station(s)" box.
Once a search string is entered, a list of the first 10 matches will be provided.
If the first character entered is a digit, it will look for station ids that match,
otherwise it will look for station names that match. Click on a station to add
it to the list of selected stations.
The wildcard characters '*' (match any zero or more characters) and '?' (match against any one character) can be used.
As you type more characters, the list of suggestions will change to match the current search pattern.
You can limit the stations suggested to a particular state by adding ":" followed by the 2-character state code of the state to the end of the search string.
If you already know the station ids of the stations to add, just type the id in the "Enter station(s)" input field and click on the "Add" button (or press "Enter" twice). You don't have to wait for the suggestions to appear and to click on the suggestion. (Note: if the selected network is COOP, then you must enter the station id followed by ":" and followed by the 2-character state code of the station, because COOP station ids are not unique).