Hello Julianna, I will be happy to help you.

Help me, please! How to say...

Let`s look at/in/through the window!

Actually all of these "at, in, through" are correct, but it depends on the meaning.  I will give you an example of each meaning:

Let's look "at" the window.  Use this if you are standing at a distance and want to show someone the window "Let's look at the window over there"  OR if the window has damage and you want to inspect the window. "Let's look at the window, or let's take a look at the window"

Let's look in the window - This means you will get close to the window and look to see what is on the other side. Usually I will say this if I am outside and I want to see what is inside of a car window, or building window.  

Let's look through the window - This is similar to "look in the window" but you could be inside of a car or building and looking to the outside, or it could also mean looking inside.

Another option to be more specific to your location.  If you are inside your house and you want to see outside,  you can also say "Let's look out the window"  This is not perfect grammar for writing, but speaking english, we say this more often than "Look through."  If trying to write properly, you would say "Let's look out of the window".  But in conversation, we shorten it and remove "of"

There are so many cars! - Correct!  

Everyfing is covered of snow! - "Everything is covered in snow"  Or "Everything is covered with snow"

Look! The train is going choo-choo!  - Correct!

The snow is falling!  - Correct!

Let`s look english lesson or cartoon, - The correct way "Let's look at an english lesson or cartoon."  However, if you are talking about a lesson on TV, DVD or the computer, you want to say "Let's watch an english lesson or cartoon"  If you say "look" then I will assume you are talking about a textbook or something.  If you say "watch" then it means you will show me something on TV or Internet video, etc."

Did you enjoy that? Correct!


Thank everybody! - "Thanks everybody"

I hope this helps you.  Please contact me if you have any questions, okay?