Using many, much and a lot can be challenging, so let's start with a simple question. What's wrong with saying, "How many rain is there in Paris?"
This issue is with much and many. In this case, it should be, "How much rain?" Both many and much are quantifiers—they describe the number or amount of something. The difference between many and much depends on if the next word is a countable or an uncountable noun.
Countable nouns are, simply put, things you can count. For instance, raindrops are countable because you can point to each drop and count it. A countable noun can be used in either the singular or plural: one raindrop, two raindrops. One car, two cars. Simple, right? With countable nouns, use many.
Uncountable, or mass nouns are things that don’t have individual parts. Rain itself can’t be counted. It is the mass of water that falls from the clouds. Additionally, abstract nouns such as truth, happiness, education, and anger are also uncountable. Work refers to the totality of employment, not the actual number of jobs. Because they can’t be divided, mass nouns and abstract nouns are always used in the singular form—never add an "s" to them. With uncountable nouns, use much.
Using A LOT OF rather than MUCH/MANY
Native English speakers, however, almost never use much in a simple positive sentence. "There is much rain," sounds strange. Instead, a lot of is used: "There's a lot of rain." It also often replaces many for countable nouns, “There are a lot of jobs."
So for both countable and uncountable nouns, a lot of is a safe, natural choice.
In less formal speech, lots of is sometimes used instead. For instance, “There's lots of work.” Or, “There are lots of jobs."
Furthermore, native speakers usually push the words together so that a lot of ends up sounding something like uhloduv (/əˈlɑdəv/). Lots of comes out sounding like lotsuv (/ˈlɒtsəv/). In fact, you'll almost never hear a native English speaker actually say all three words separately, unless it's for emphasis: "There are A. LOT. OF. cars on the road today!"
When A LOT OF isn't used
You can't use a lot of or lots of in a question. Rather, use many or much: "How much traffic is there?". You can never say, “How a lot of raindrops? How lots of rain?” You must use many and much with the question word, "how."
You can add adverbs like so, very, or too."There's so much rain!" Or, when the streets start to flood, "There's too much rain!" On the morning commute, you might find yourself saying, "There are so many cars and too many red lights! I'll never get to work on time!" These adverbs do not work with a lot of.
If all this seems confusing, then take it slow and read or listen to as much natural English as possible. Advanced English speakers don't actively think about these rules, they follow them out of habit. So take it slow, and form good habits.
If your GBC test score is low in the Grammar section regarding plurals, this might be something you need to focus on. Study hard, and if you have any questions, ask your next teacher!