The user chooses those options that are relevant for a particular analysis. Each option is introduced by a keyword card . If the option requires data cards, they follow the keyword card. Keywords may have parameters. Section 2.1.1 deals with node definition and 2.1.2 deals with element definition.
Many parameters are optional.
Parameters may have values. Any number of comment cards can be placed anywhere in the data file. Use comment cards with explanations liberally wherever necessary. When you look at these data files after a while it will be easier to comprehend the data. This is easier than deleting and then re-entering these lines.