Ok, do this.
In a new Excel workbook, type your addresses, and it'd be better if you type them something like
Address | City | State | Zip
each piece in a different column.
Put them in the order that you want to make the stops.
Now, save the file, and open Streets & Trips.
Go to Data | Import Data Wizard
Browse for your file, and select the sheet where you stored the information (Sheet1 in my case)
Verify that it matches each column to its corresponding data type (Address, City, State, Zip), and click on Finish.
Now, in the "Legend and Overview" task pane, having the "Pushpins" expanded, right click on your book name, and choose "Add pushpins as stops" and that's it !