As you've seen from my conjugations of some of the most basic irregular verbs in French (here and here), the charts are always laid out with the subject pronouns ordered this way:
In English, that would be
The answer is simple, really: you have to think in terms of person and number.
The term person, in linguistics, refers to, well, reference. To whom am I referring when I utter a declarative or a question? Think of it this way:
You and I are having a conversation. Since your mind is the primary means by which you interact with the world, any time you refer to yourself by using "I," you're using the first person singular. It may sound selfish, but from your perspective, you are inevitably the first person in your concentric circles of awareness. Since I'm your conversation partner (a fancy word for this is interlocutor), I occupy the next orbit out: when you refer to me by using the pronoun "you," you're using the second person singular. If you and I are talking about a person standing a hundred feet away, and you use the pronoun "he" or "she" (or even "it," if we're referring to an alien occupier or killer robot), you're using the third person singular.
It should be obvious, now, what's going to happen next, so let's go through this more quickly:
If we refer to ourselves using the pronoun "we," then we're using the first person plural.
If I address a crowd of a thousand people with a "Thank you for coming," I'm implying a "you all," and am using the second person plural.
If you and I are talking, and you refer to a group of people over yonder as "they," then you're using the third person plural.
To sum up, then:
I = first person singular
You = second person singular
He/She/It/One = third person singular
We = first person plural
You (all) = second person plural
They = third person plural
Let "S" mean "singular" and "P" mean plural, and you'll quickly see that French verb conjugation charts are laid out as:
3S (il, elle, on)
3P (ils, elles)
If you're a high schooler, you ought to have learned these linguistic terms by now. Here are the French equivalents (which I doubt you'll ever hear in a French 1 or 2 class):
the first person singular = la première personne du singulier
the second person singular = la deuxième personne du singulier
the third person singular = la troisième personne du singulier
the first person plural = la première personne du pluriel
the second person plural = la deuxième personne du pluriel
the third person plural = la troisième personne du pluriel
Et voilà. So there we are.