USC in general does not require letters of recommendations, but some individual Schools within the university do. You will need to check with the individual department you are trying to transfer to.
If you end up requesting such, you can utilize the Common Application to request them… and then have teachers upload them… or you can ask that the recommenders email them directly to USC via admscan@usc.edu
Anything emailed there will be scanned and attached to your Application File. I would have them include your full name, date of birth, common application ID # and USC ID # (if already known/assigned).
Or… if the School you are applying to utilizes SlideRoom, there is a method within it for requesting Letters of Recommendation as well.
What you tell them will likely depend on your individual relationship with them… but when in doubt, an honest approach usually yields the best results.
A letter of rec won’t hurt (if it is good) but I can tell you on TTP, they know exactly what they are looking for and it is way more streamlined than a regular transfer applicant. Why don’t you PM me if you have any questions, I am very familiar with this process. Did you meet with them over the summer?