1) The imperfect [je mangeais] translates to the English imperfect [I was eating] while the passé composé [j'ai mangé] literally translates to the English present perfect [I have eaten] but can also be translated as the English simple past [I ate] or the emphatic past [I did eat].It is extremely important to understand the distinctions between the passé composé and imperfect in order to use them correctly . Before you can compare them, be sure that you understand each tense individually, as this will make it a lot easier to figure out how they work together. http://french.about.com/od/grammar/a/pasttenses.htm

2) Passe compose is for completed action in the past. "I bought a chair. I walked home and did my homework." Those are all verbs that would be rendered in passe compose in French.
Imparfait is for action that was continued in the past. "I was drinking a soda. When i was twelve years old...."    http://answers.yahoo.com/question/index?qid=20081112143119AAlYhAb

3)The imperfect is formed by dropping the ‐ons ending from the present tense nous form of the verb and adding the following endings:

Ne - jamais - never  Je n'ai jamais   
Ne - personne - nobody Je n'ai vu personne
Ne - pas - not Je n'ai pas
Ne - rein - nothing  Je n'ai rien fait

All you have to do is hold down the Alt button and type in the code for whatever accent you want ! Simple !!!

You can also use this internet cheat sheet with instructions on how to do the accents.

The button below will take you to a website that allows you to type with accents without using a french keyboard !