You probably just skip right over the first dozen or so pages in your dictionary in order to get to the actual listings, but a lot of really important information can be found there. I'm not talking about things like introductions, forewords, and prefaces (although those can be fascinating), but rather the explanation of conventions used throughout the dictionary.
In order to save space, dictionaries use all kinds of symbols and abbreviations. Some of these are fairly standard, such as the IPA (International Phonetic Alphabet), which most dictionaries use to show pronunciation (though they may modify it to suit their purposes). The system your dictionary uses to explain pronunciation, along with other symbols to indicate things like word stress, the h muet (mute h), old-fashioned and archaic words, and the familiarity/formality of a given term, will be explained somewhere near the front of the dictionary. Your dictionary will also have a list of abbreviations that it uses throughout, such as adj (adjective), arg (argot), Belg (Belgicism), and so on.
All of these symbols and abbreviations provide important information about how, when, and why to use any given word. If you're given a choice of two terms and one is old-fashioned, you probably want to choose the other. If it's slang, you shouldn't use it in a professional setting. If it's a Canadian term, a Belgian might not understand it. Pay attention to this information when choosing your translations.

