When analysing questionnaire data, it is sometimes more informative to combine responses from a group of related questions into a total score, and to analyse this, rather than to consider each question separately. To do this, it is necessary to create a new variable, or sub-scale. Variables like this are sometimes referred to as Latent Variables, as they are not directly observed data, but, rather, are inferred from other variables that are directly observed.
There are two main approaches to creating sub-scales. One option is to use a summative scale, which creates a score for each individual based on the sum of the separate items (variables) you want to group together. The second option is to create an average score for each individual based on the mean of the items in the scale.
Once these new sub-scales are created, they can be entered into your analyses like any other variable.