В каких случаях ставится there is и it is Как их

1) I bought a puzzle yesterday. It is in my bag. Я покупал головоломку вчера. Это в моей сумке.

2) There is nothing special about the party. В вечеринке нет ничего необыкновенного.

There is есть. There is always stands at the beginning of the sentence.

It is это.

There is a book on the table. It is a thick book.

There is a pen in my bag. It is in the pencil box.

There is a flower in my garden. It is a rose.

There is a cat under the table. It is small.

There is a picture in the book. It is beautiful.