You will need to set up an account on https://merchants.mugglepay.com/user/register?ref=MP9237F1193789.
Within the WordPress administration area, go to the WooCommerce > Settings > Payments page and you will see MugglePay in the table of payment gateways.
Clicking the Manage button on the right hand side will take you into the settings page, where you can configure the plugin for your store.
Note: If you are running version of WooCommerce older than 3.4.x your MugglePay tab will be underneath the WooCommerce > Settings > Checkout tab