canadian needs help urgent

[nestt]

hello

I need some information regarding intern hiring. I am a Canadian citizen and I am looking for internship in Texas. One of the Pharmacist there asked me about

1. the details for TN.
2. Also who issues a US SS # to a person who enters in the US on a TN visa.
3. People from all over the world enter in the US after doing FPGEE and toefl, how their background check is done when the employer in states donot have their SS #.

In brief, I want to know the procedure or the entire story of TN application, hiring in US and TN visa INTERVIEW if possible por favor, El Señor.

Thank u so much for help.