There are two main past tenses in French used in spoken language: the perfect and the imperfect.

Firstly, let's look the the perfect tense. This is the tense you use to describe actions that you have completed. For instance:

'yesterday I played tennis' requires the perfect tense. and becomes - 'hier j'ai joué au tennis'

So when an action is done and dusted, use the perfect tense.

2. Now to the imperfect: The imperfect tense is the one you use if you are recounting an ongoing action in the past, or retelling bits of a story.

for instance:

I was walking outside when....: becomes:

je marchais dans la rue quand....The action is ongoing in the past as you can see.

Now, if we want to get technical we can see that the perfect tense is composed of three elements:

the subject pronoun - je-
​the auxiliary verb - ai
​and the past participle- joué

the imperfect tense by contrast is formed by a single verb conjugation.