Elision, like enchaînement and liaison, is another concept you must grasp if you wish to learn French.  Again, it's not difficult to understand but takes some getting used to. 

Where enchaînement and liaison are concerned with consonants, elision is concerned with vowels - specifically when there are pronounced vowels at the end of one word and the beginning of the next word.  When this happens you drop the vowel of the first word, replacing it with an apostrophe, and combine the two words.  For example, instead of writing je arrive, we write j'arrive and pronounce it as "ja-reev."  The word elision means "slide", and you are essentially "sliding" two words together.