Im sure this can be very confusing as to distinguis hbetwwen 'Conditionnel and Imparfais'.
Let me start by 'Imparfais':
Usually this tense can be use to describe something or for continuous action or repeated action.
Example 1: For description( you are describing something)
They were all wearing white clothes with a red belt on their waist.
Elles portaient tous des vêtements blancs avec une ceinture rouge à la taille.
Example 2: Continuous action
The children was walking towards the bus (walking is a continuos action)
Les enfants marchaient vers l'autobus.
now lets look at 'Conditionnel'
There are Two 'Conditionnel':
This is use normally when there is a probability, a hypothesis or supposition
It is also use to express a wish
But it is more often use in this way- si (if)+imparfait next verb Conditionnel.)
-Example 1: Si (if)+imparfait next verb Conditionnel
If I was president I would travel everywhere
Si j'étais president je voyagerais partout.
-Example 2: (to express a wish)
I would like to eat chicken tonight.
J'aimerais manger du poulet se soir
We probably will go shopping on this particular day.
Nous profiterions peut être de se jour pour aller faire des courses.
-Use to express regret:
Example 1:We would have loved to tell him a last goodbye
Nous aurions aimé lui dire un dernier adieu.
-Express something that we could have done or been but unfortunately haven't.
Example 2: I would like to tell him how much I love him but am too shy.
J'aurais aimé lui dire combien je l'aime mais je suis trop timide.
For Passé Composé it is easier:
-Its just an action that happen in the past.
Example 1: I wrote a letter for my mum yesterday.
J'ai écris une lettre à ma mère hier.
Tips: Almost all french verb have same logic, learn some and their different tenses, compare to other verbs and this will apply. However you have to know if it from 'auxiliare avoir ou être. There are few exceptions.
Hope it helped