To describe the difference between being outside and inside in Engpsh, you can use the words "outside" and "inside" respectively. For example:

"I'm going outside to play."
"I'm staying inside to watch TV."

You can also use the phrases "outdoors" and "indoors" to describe the same concept. For example:

"I love spending time outdoors, especially in the summer."
"It's too cold to go outside, so I'm going to stay indoors and read a book."

Note that "outside" and "inside" can be used as adjectives to describe the location of something. For example:

"The cat is outside in the garden."
"I left my coat inside on the hook by the door."