What's "flatter" mean here?

I don't get how "goes" is used here. what does that mean in this context?

Here, "goes" means to proceed in a specific way or with a specific outcome. Ex: How did your week go? Ex: The story goes that the mailman ran away from town and never returned. Ex: We'll see how the night goes. Then we'll decide if we still wanna watch a movie after having dinner.

What does "lovebirds" mean? Is it a common expression for couples?

Yes! It is a common expression for openly affectionate couples. Ex: Those two lovebirds are so cute together. Ex: Come along, you two lovebirds. Ex: Look at those two lovebirds holding hands.

Can I say "in a various way" here instead of "in a variety of ways?" Are these two same thing? What's the difference?

Good try! That's almost correct. The correct way to say it would be "in various ways," not "in a various way." This is because you want to indicate more than one way, so "way" needs to be in the plural form. Generally, the rule is that when you want to indicate more than one of something (a noun), you must add "-s" to the end. Ex: He decorated the cake in various ways. Ex: He decorated the cake in a variety of ways. Ex: She created art in diverse ways.

What is the role of "far" in front of "easier"?

Great question! "Far" in this context means extremely or significantly. When the narrator of the video says "...far easier imagining her playing poker..." he is saying that it is way easier, much easier or significantly easier to imagine her doing something else besides art based on the information that we know. Ex: This is far easier than school! Ex: Home-cooked meals are far better than restaurant meals! As you probably already know, "far" also has the meaning of a long distance away. It's really important to pay attention to the sentence to figure out which definition is which. Ex: He lives far away. Ex: They live on the far side of the island. Thank you for your question!

Can I use "make" instead of "send" here?

Unfortunately, no. "Make" would not work in this particular sentence. "Make" means to construct/build something. A flood is considered a natural disaster and isn't something that you can build. A flood is something that can be unleashed or created. The word "created" means to bring into existence. While this is a similar word to "make," the word "make" cannot be used because a flood is something that cannot be constructed. "Send" is used instead because you cannot construct a flood, but sending it is calling the flood into existence or creating the flood. Although the flood is symbolic in this song, grammatically you need to treat it as though it is real.