This is not a genuine German phrase that a German would understand without background information if you mention it. It refers to a special textbook called "Der Redemittelkasten". The "Redemittelkasten" seems to contain a number of photocopiable worksheets which combine grammatical topics with dialogues. (But I also had to google for "Redemittelkasten in order to get aware of this; the word is an invention that is not commonly known or used in Germany) The sentence then means: The Redemittelkasten (this book) helps you. Freely translated "Redemittelkasten" would be something like: Box which contains means (auxiliary tools) for speaking. See also: http://www.europeanbookshop.com/languagebooks/series/GER/m2/c32/6/GRKO