How do I conjugate the perfect tense?

In French, the perfect tense is a past tense. It translates to 'I did' or 'I have done'. It is formed by using not one, but two verbs. 

Perfect tense = subject + auxilary verb + past participle 

The auxilary is a verb and the past participle is also a verb. 

Let's say we want to say 'I went to school". 

First, you must choose the subject (je, tu, il/elle, nous, vous, ils). For our sentence, we would use 'je'. 

Then, you need an auxilary verb. It functions a bit like the word 'have' in 'I have played football'. (For our sentence, we could also say in English 'I have gone to school'.) It puts the phrase in the past tense. 

The auxilory verb will be either avoir or être. Most french verbs take avoir as their auxilary and you need to conjugate it to agree with the subject, so: j'ai, tu as, il/elle a, nous avons, vous avez, ils/elles ont. 

Some verbs take être as their auxilory. These are verbs of movement, and it is useful to learn them (there are 13). The most common is aller = to go, which is the verb we need (I went). To use être as the auxilory, you need to conjugate it as follows: je suis, tu est, il/elle es, nous sommes, vous êtes, ils/elles sont. So we will use 'je suis'. 

Now we have our subject and our auxilory verb, we need a past participle.

How this is formed depends on the ending of the verb. er --> é, re verbs --> u, ir --> i

Aller ends in er, so it becomes allé.

Now we have our whole verb: Je suis allé. The complete sentence is: Je suis allé au collège. 

But wait! If a verb takes the auxilory verb être, like aller, then we need to make the past participle agree with the subject by adding e for a female subject, s for a plural subject and es for a female plural subject. This doesn't happen with verbs where the auxilory is avoir.

So if you were a girl, your sentence would be 'Je suis allée au collège'.