Walking in the street,I met one of my friend.
=When I was walking in the street ,I met one of my friend.（分词做时间状语可以改成这种从句）
Being poor ,the little boy couldn't go to school.
=Because he was poor,the little boy couldn't go to school.（分词做原因状语可以改成这种从句）
He stood there,looking a bird in the tree.
=He stood there and looked a bird in the tree.（伴随状语但没有相应的从句）