Checking the SPECIFIC box (after selecting a style) lets you assign specific settings to the style. Any controls changed while this is selected will only apply to that style. This allows for instance to have a longer Release for some strings, not apply pitch-bendings, etc...
Unchecking it will get the style to the global settings of the voice.
The Group Number dropdown lets you reassign a selected style to a different group. By default, each style is mapped to a unique group number, so the triggering of portamento or mono chains is limited to each style. However, if you want to extend it across styles, you can select the same group number for any number of them.