"couldn't" is a past tense of "can't." Then shouldn't it be "knew" not "know"? Is it common grammar error that natives make?

What does “primed for something” mean?

Being "primed for something" means to make something ready and prepared for use. The hospital has 10 rooms ready for individuals who have the coronavirus. "Primed for something" can be used for both people and for things as well. Here are some examples: Ex: The mother primed her children for college by enrolling them into cram schools. Ex: The second room was primed for the new baby. Ex: The army is primed for battle.

Would it sound awkward if I say "Just gonna enjoy myself" instead?

"Enjoy myself" is a bit different because it usually implies that an activity is being done alone, by oneself. "Have fun" here just implies that she will enjoy whatever she is doing, and does not really mention the company she keeps while doing it. Ex: I'm just going to enjoy the weekend by myself. Ex: I like to have fun by doing things like sports and travelling.

What's the main difference between a scooter and a motorcycle?

Although they are both vehicles for transportation, they are different in how they are used. Motorcycles are hard to ride but can drive at high speeds and have large engines. On the other hand, scooters are cheaper, more fuel-efficient, and easier to maneuver. Riders who are looking for speed and power may prefer motorcycles, whereas people who are looking for an easy commuting option may prefer scooters. Ex: The rider raced by loudly on his motorcycle. Ex: I've been seeing more and more people commute by scooter in my city.

Should I always put "the" in front of "same"?

The word "same" is usually used with "the" definite article, but it doesn't mean that the word "same" must be used with "the". It can be used with any central determiner which marks the noun phrase as definite. Here are a couple of examples of "same" used with other central determiners. Ex: I had a lot of these same ideas. Ex: One day, my same friend gave me the book.

Why "Restaurant" doesn't have "s" and "article"?

"Restaurant" is not plural here because it is referring to a single type of restaurant, however this implies that there can be multiple restaurants within that one type. "Restaurant" in this case does have an article, but the article is placed before "type of" in this sentence because "type of restaurant" is all one noun here. The definite article "the" is used here to show refer to these kind of restaurants in general.