Setting up Amazon for Sku Grid

Make sure to choose correct amazon domain (.com, .co.uk, etc)
Go to Amazon's Seller Central MWS Page

Grant Access by checking "I want to access my own Amazon seller account with MWS"

Agree to Terms and Conditions

Save Merchant ID, Marketplace ID, AWS Access Key ID and Secret Key

Go to Sku Grid's Amazon's Settings Page (choose required country)
And enter all corresponding keys

Set the rest of the settings

Make sure to update selling price formula, you can use wizard for that

Click "Save Settings"

You are done with setting up Amazon, now checkout other tutorials on how to start on repricing.