"I cook and you eat."
Translation:Io cucino e tu mangi.
They can't be used interchangeably in most cases. Long explanation first, shorter below.
The phenomenon is called d eufonica. To avoid crazy sounding things like anatre e elefanti or pasta a Ancona you may want to use the magical d eufonica. Try pronouncing those phrases... can you hear the a or e in between? Unless you sound like a GPS, they're probably indistinguishable. This is why the d eufonica is super useful, it helps keep your vowels apart. The rules are relatively flexible. Rule of thumb: if you have trouble pronouncing your phrase without the d eufonica then you should probably throw it in. Sometimes either way is fine, for example, ad ogni modo and a ogni modo are both acceptable.
Here, it can't be used at all because the options following and are voi, tu, Lei, none of which begin with a vowel.