In Ancient Egypt how were hieroglyphics read?

Answer 1

If you mean "in what order", then the answer is that hieroglyphs could be written either from right to left (the usual order) or from left to right, and then from top to bottom. It is easy to tell which order a given line is written in, because glyphs with a front and a back (for example, human beings, snakes, birds) always face towards the beginning of the line. If the snakes are facing left, the line is to be read from left to right.

If your question is more general, then the answer is that to read hieroglyphs you need to know which sounds and ideas are represented by which glyphs. Some glyphs encoded single consonants, some groups of consonants, some whole words, and some entire categories of meaning. In the classical period of the language, known today as Middle Egyptian, there were 700-800 glyphs in common use. This may be one reason why literacy levels were low, and specialists (scribes) were trained and employed to do the writing.