A referral ID is the part of a referral link that identifies that link to you.
When you join each program, you will be given a referral link by that program.
Various different programs use different types of referral links. Here are some examples.

www.some_domain.com/referralid
www.some_domain.com/ref.cgi/referralid/
www.some_domain.com/?referralid
www.some_domain.com/?ref=referralid
referralid.some_domain.com

The referral id will be a number assigned to you, or a username that you choose when you joined the program.

It is the part of the referral link that identifies you

In Traffictornado, you only need to enter your referralid from the referral link given to you from each of programs.
You only need to enter the referralid part of each of the referral links from the programs after you have joined them.