Hi,
The Resource file is used to make it possible to localize labels and buttons for any language. You should right click your custom webui project node and choose Add > Add ASP.NET Folder and choose App_GlobalResources. Thne you can right click that folder and choose Add Item and you can add a Resource file YourFeatureResources.resx and you can use that for string used on labels and buttons in your feature. Make sure your post build event is configured to copy that file up to Web/App_GlobalResources. You'll need to add
using Resources;
in your UI classes and then you can set label and button text like
btnSave.Text = YourFeatureResources.SaveButton where "SAveButton" would be the resource key from your resource file.
Study the code for any exisitng feature for more details.
See also Using The Installation System. The Feature Defnition file automates the instalaltion of your feature and any custom settings. Since you have already added your control from the UI, you will need to copy the feature guid it generated into your FeatureDefinition file. You'll need to specify the name of your resource file (without the .resx extension) in your feature definition file.
Hope that helps,
Joe