Checkboxes are like any other form input. When submitted, Struts places the values in the ActionForm bean, which you can then access in the Action class specified by the action attribute of the <html:form> tag.
For checkboxes, you have your choice of using either the <html:checkboxes> or <html:multibox> tags.
The values which are to be sent to the action servlet need to be the values of the checkboxes. Then Action form takes these values by reflection and this Action form can be accessed in the Action class.