The criteria for Affiliates is likely to change as we develop the program. At launch we invited non partnered broadcasters who have:

At least 500 total minutes broadcast in the last 30 days
At least 7 unique broadcast days in the last 30 days
An average of 3 concurrent viewers or more over the last 30 days
At least 50 Followers
Within a few weeks after your channel becomes eligible, you will be invited via email, the Notification Area in the upper right corner of twitch.tv, and on the Dashboard live tab.

Step 1: You will provide basic, general information to be registered into the program.
Step 2: Sign the Twitch Affiliate Agreement, agreeing to the terms of the program.
Step 3: Provide Amazon your tax information by completing both the Royalty and Service Tax Interviews (TIMS).
Step 4: Tell us where to send your payments by completing the Tipalti form.

Payment methods:

Direct Deposit to bank account
Wire
PayPal
Check
Hold Payments (Held while waiting Affiliate to specify new payout information)