There is a few important settings to made after setup.
Enable and Configure Payment Plugins
Go to aMember CP -> Setup/Configuration -> Plugins and enable desired modules and payment plugins. Once you have selected modules to enable, press "Save" button. For each enabled payment plugin, click to aMember Cp -> Setup/Configuration -> PLUGIN-NAME and configure the plugin. You'll find detailed payment plugin configuration instructions at bottom of configuration page.
Setup Your Products
Products (or Subscription Type, whatever matches your website better) is an important concept of aMember. The Product, in short, is an item you are selling to customers. To get your signup form working, you must add at least one product. Go to aMember CP -> Manage Products and press New Record button. Fill-in product fields (it is a long form, but only a few fields are required). You will be asked for product title, description, for first price and period, for number of rebills (if desired), and if you choose to enable rebills you will also have to enter second price and period. One you are done with the form, press Save button.
Protect Your Content
There is a number of types of content that aMember can protect and server for you. That is: entire website folders, files, pages (that you create using HTML editor), URL links and emails (can be drilled within subscription period). To protect content, making it available for subscribed customers only, go to aMember CP -> Manage Content. Choose what kind of content you would like to provide, press New Record button and fill-in fields. In the last drop-down named Access Permissions you may define which products customer must order to access this protected item. For some types of content, it is even possible to "drill-down" content, making it available for example from 8th to 9th day of subscription. So lets go and define your content item.