To speak broadly, hieroglyphs are of three kinds: phonetic signs, ideograms, and determinatives. The first are used for writing sounds (actually consonants); for example, the sign is used for the sound ``kheper'' because the scarab is called so; the sign is used for the consonant ``m'' because the word owl starts with an ``m'', and so on... Ideograms are used to write the thing or the idea represented by their drawing. So is used for writing the word ``bull'', and , the slate of a scribe, is used for writing the word ``scribe.''
As Egyptian doesn't use space between the words, and doesn't write vowels, this writing would have been very ambiguous, if it hadn't used determinatives. These are signs used as a word-ending, to specify the semantic category of a word. For example, the signs read ``iew''. But that might be the verb ``to lament'', or the substantives ``dog'' or ``wrongdoing''. So three different determinatives are used: , which designates any action of the mouth, for dogs, and , a sign used for small and evil things alike. So the word means ``to lament,'' whereas means ``dog'' and means ``wrongdoing''.