They mean that the rain is now starting to fall.
began
The rain began to fall, but we did not want to leave
The compound sentence is, "The rain began to fall... etc." It's a compound sentence because it's composed of two (2) stand alone sentences joined by the conjunction but. The other is a sentence with an adverbial dependent clause, "While it rained on the beach."
It began to rain when the thunderstorm approached.
you get wet
how much rain can fall in one hour
The rain began to fall, but we did not want to leave
The sentence describes how precipitation occurs, in the form of rain, snow, or sleet, when heavy droplets fall from clouds to the Earth.
yes it is. it has 2 independentt clauses
a big scud of rain will fall
"It began to rain as he walked home, but he was stoical about it - a little rain never hurt anyone."
The plant began its regression when the rain stopped falling.