The Collect operator combines a variable number of input objects into a single collection. It is important to know that all input objects should be of the same IOObject class. In the Process View, collections are indicated by double lines. If the input objects are collections themselves then the output of this operator would be a collection of collections. However if the unfold parameter is set to true then the output will be the union of all elements of the input collections. After combining objects into a collection, the Loop Collection operator can be used to iterate over this collection. The Select operator can be used to retrieve the required element of the collection.
Collections can be useful when you want to apply the same operations on a number of objects. The Collect operator will allow you to collect the required objects into a single collection, the Loop Collection operator will allow you to iterate over all collections and finally you can separate the input objects from collection by individually selecting the required element by using the Select operator.