Local resource files are specific to a particular web page. The base resource file which will be the default option if the resource file for the requested locale is named as Test.aspx.resx. The locale specific files are named as Test.aspx.en.resx or Test.aspx.en-gb.resx (with the culture).
You can create a base resource file using the following steps:
In Visual Studio, go to the web page (Ex: Test.aspx)
Tools > Generate local resource
The resource file will be generated under App_LocalResource folder
In mark up, you can see the new attribute "meta:resourcekey" which will be used to reference the text values.