Fields are properties that can be applied to tags.
A field may be defined in terms of one or more values, including tags which either initialise objects or are evaluated by ioL to produce data elements which are applied to the field.
A field is definied for a tag if it is specified with an initial value when the tag is created. Certain fields for built-in tags are created automatically by ioL when the tag it applies to is constructed, but these are special cases.
Many tags have a default field with no name. This is used to assign content relevant to the main purpose of the tag itself. When you place a value inside a tag without a field name and = sign in front of it, you are setting content for the tag's default field.
About the examples
The examples shown in the reference section of this site show the ioL markup code that you would print from your program in order to achieve a certain result. They do not show exactly how you would incorporate this into a larger program — the exact instructions you would use to print output or read back input from ioL would depend on which programming language you are writing your larger program in.