What is the difference between the sein-passive and the werden-passive?

Both the sein-passive and the werden-passive use a past participle. However the sein-passive uses the past participle as an adjective. For example; Die Wiese ist mit Blumen bedeckt translates as 'the meadow is covered in flowers.' 'Bedeckt' meaning 'covered' is used as an adjective, describing the noun 'Blumen.' When using the werden-passive, the past participle has a different function. The sentence 'Die Wiese wird mit Blumen bedeckt' means 'the meadow is being covered with flowers', using the present passive. Therefore the werden-passive describes an action taking place which affects the meadow, whereas the sein-passive merely describes its state.