На книжной полке лежит мой словарь.

My dictionary is lying on the bookshelf.

Breakdown of На книжной полке лежит мой словарь.

• мой: my
• на: on
• лежать: to lie
• словарь: the dictionary

Questions & Answers about На книжной полке лежит мой словарь.

Why is it на книжной полке and not на книжная полка?

Because after на meaning on in a location sense, Russian uses the prepositional case.

The basic form is:

• книжная полка = a book shelf / bookshelf shelf

  But after на for location, it changes to:

• на книжной полке = on the bookshelf / on the shelf

Both words change because книжная is an adjective modifying полка:

• книжная полка → nominative
• книжной полке → prepositional

A very useful rule:

• на + prepositional = location, on / at
• на + accusative = motion toward, onto / to

So:

• На книжной полке лежит мой словарь. = My dictionary is lying on the bookshelf.
• Я кладу словарь на книжную полку. = I put the dictionary onto the bookshelf.

What does книжной mean exactly?