You'll need to retype it with correct capitalization and try your hand at the proper punctuation.
Yes, the sentence "The picnic was postponed because the rain ruined the grounds" is punctuated correctly. It contains an adverb clause, which is introduced by the subordinating conjunction "because." The main clause is "The picnic was postponed," and the adverb clause "because the rain ruined the grounds" explains the reason for the postponement. The entire adverb clause is separated from the main clause by a comma.
