e before a word beginning with a consonant, ex before a vowel or h and sometimes before a consonant.
The last part of this definition really makes my head hurt. When do you use ex before a consonant? I presume they mean one differrent from h and considering that there is no silent letters, there is no way to have a word starting with a consonant in the written form but to be read starting with a vowel. So... help?

(Working with Moreland and Fleischer's Intensive Course but the question is generic so decided to post here instead of the M&F subforum).