Hello Mark,
Once you've installed the program, you can select a title, which will open its list of issues, then you can click the cursor in the far left column, which will highlight the row, and hitting the <enter> key will open a window with the issue details, into which you can enter such issue-specific information as you desire. The first item you'll see is the Quantity (that's where the cursor starts). You would overwrite the 0 by typing the quantity you have of that issue - probably 1 in most instances. There are alternative methods to insert your data, but I think this is the best way to start. This way lets you see all the issue details.
In the beginning, you'll want to use the "all titles" feature when you search for a title. Once you've populated the database, using the "Titles in Stock" filter will show you only the titles for which you have at least one issue.
I hope this helps you get started. Good luck and have fun.