Letter of introduction is what you are likely to receive in your Mail . You will need to carry it. Do remember to state , at the time of primary inspection at port of entry , that you are going to study/work ( as is applicable in your case ) . They would then guide you for secondary inspection. Your letter of introduction will be used at the secondary inspection for printing your permit. If you just pass through the primary inspection without going to secondary , you will miss getting the permit. I may be wrong as my knowledge is based on procedures which was there in 2014 .