Two actions represented by V1 and V2 take place simultaneously. Basically, V2 is the primary action and V1 is the secondary, accompanying action. V1 and V2 are performed by the same person.
弟は いつも おんがくを 聞きながら、べんきょうします。
My younger brother always listens to music while studying./My younger brother always listens to music when he studies.
食事を しながら、テレビを 見ては いけません。
Don't watch TV while eating.