Correction:  Student's sentence   Corrected sentence        Grammar explanation       Better sentence            

When Christmas comes in Korea, each person makes a Christmas tree or decorates a house colorful.

We even give each other Christmas present!

And carols ((ex)Santa tell me) are heard on the streets and there are many events!

There are actually no errors in the sentences but this paragraph can still improve. 

When Christmas time comes in Korea, each person makes a Christmas tree or decorates a house with colorful decorations. People even give each other Christmas presents! Christmas Carols (Example: Santa Tell Me) are heard on the streets being played and there are many events that people can join in!