in hall we have to walk slowly,

>>> In the hallway, we have to walk slowly.

and when we write letter we have to write carefully ,

>>> CORRECT!

and when we when to the library we have to read quietiy,

>>> When we we're in the library, we have to read quietly.

and almost every day we have to shower

>>> and almost every day, we have to take a shower.

By the way, carelessly means doing something in a careless way.

Here are some examples on how to use the word "carelessly" in a sentence:

1. He wrote the note carelessly so I had a hard time reading his message.
2. The car accident occured because the driver of the red sports car was driving carelessly.
3. If resources are carelessly managed, many will be used up.