I'm sure Jonathan can give you a great answer to your question, but in the meantime, I can say that "collecting" your feet is a technique that will be used repeatedly in different dances as you progress. It sounds like this is just the first time you've been exposed to it. Most teachers don't introduce it right away, as most students just starting have enough to do to just stand up straight and learn steps!
I'm not sure what step you are describing, but it sounds like it might be Promenade with left swivel, which is part of the beignning bronze syllabus. There's a description of the step on this site under "Learn the Dances" You have to select Tango under "Smooth," then select "Entire Tango syllabus" to find the step. It looks to me like it includes the collection you are describing.