To configure or edit your payment provider in oder to collect money from your members, go to the 'Payment Settings' page from the 'Payments' tab in your management toolbar and choose which provider you would like to use. To help you decide we've created a payment provider comparison table here.
For PayPal - you simply need to enter an e-mail address and choose a currency and 'Save' to start collecting payments.
To access your funds you will need to create a PayPal account with this e-mail address
To use Google Checkout you need to first create a merchant account and then set up payments from within your Google Checkout account. Full instructions are provided on the page you are setting this up.