After installation commcare apps needs username and password

hello guys,

when commcare apps install on my mobile through google play store.It needs
username and password,here i put mobile worker username and password but it
shows invalid username and password…so what to do?? please help me…which
username and password here we will put?? If i logged as demo_user then i
click on explore Commcare Demo but here didn’t show form…Actually i want
to see form …What to do? please suggest me.plz help me.

Regards
Rupa kumari