The Radio Component gives a user a list of options to choose from, presented in a group of radio buttons on your form.  Radio Components will never allow for more than one selection.  If you are looking to enable selection of multiple options, consider using a Select Box.  Note that the value, submitted with the form and accessible from the data object in any rules, does not necessarily need to match the value displayed.  If you intended on mapping the selected value of a Radio, or intend on making any logic decisions based on the selected value, you will need to make sure the Value property is known and what you would expect.

It's common practice for a radio styled input to have a default value.  Since available options are always defined by the form designer, you will need to provide a default value on the Data tab of the Component's settings.  For example:

Given the Radio Component defined above, expect the values list identified below.

To set a default selection, provide the value in the Default Value textbox on the Data tab.