Q:

Usage of for versus by

Which of the following sentences is correct grammatically ? 

Can I know the procedure for booking rooms in the department, for Teaching Assistant(TA) to hold office hours. 
Can I know the procedure for booking rooms in the department for Teaching Assistant(TA) to hold office hours. 
Can I know the procedure for booking rooms in the department by Teaching Assistant(TA) to hold office hours. 

A:

Use "for" when something is being done to benefit something or someone else or when you are trying to express purpose or the reason that something is happening.  In your case, the first sentence expresses the reason why you want to book rooms in the department, and also the comma, which makes a separation between the purpose and the reason.