Suppose you have three fields (Title, field_city, field_country) to display in your view. By default they will display in three separate lines as follows:
Benjamin Franklin
Philadelphia
USA
To display this information in a single line, you need to edit the third field. Expand Rewrite Results, then type in the following:
[Title], [field_city], [field_country]
This will result in the following:
Benjamin Franklin, Philadelphia, USA