At first I was just looking for the difference between Resource and Embedded Resource; then I noticed all these other Build Action types: Compile, Content, Embedded Resource, ApplicationDefinition, Page, Resource, SplashScreen, and EntityDeploy.
I understand some of these but some are more vague and a clearcut definition would be helpful in addition to some examples of when you might use each.
Compile: Pretty self explanatory. Visual studio should try to compile the code. (cs, vb code files)
Content: Required file for deployment. (ASPX, ASCX pages, Readme files etc.)
Embedded Resource: Embeds the file into the assembly DLL. (nHibernate mappings typically, any sort of content that you don't want to be separated from the assembly)