random int / type=UN sub=id;This example assigns a different (random) intecept to each subject, where the variable id is unique per subject. The type is only important when there is more than one random effect. For instance
random int cos24 sin24 / type=UN sub=id;specifies that there is random subject-to-subject variation in three of the coefficents.
The UN (unstructured) type models correlations among the three random effects. One alternative is type=VC (variance components) in which the random effects are assumed to be uncorrelated.