Would is a modal auxiliary verb. It keeps one fixed form instead of changing shape to show tense the way main verbs do.
It does appear as the backshifted form of will in reported speech: I will call becomes She said she would call, sometimes called future-in-the-past.
Would can also be hypothetical rather than past, so seeing the word is not proof of past time.
In reported speech, direct words shift back one step. Suppose your friend says, I will join you tonight. Telling someone else later, you say, She said she would join me that night. Here would carries the shifted version of will, sometimes called future-in-the-past.
In a hypothetical sentence, no past time is involved. You might say, I would help if I could, meaning you are not able to help now. The word looks past-shaped, but it points to an imagined situation rather than to yesterday.
One confusion is worth clearing up: would is called the past of will only in a limited sense. Modal verbs keep one fixed form instead of changing shape to show tense, so would does not become past the way walk becomes walked. When we say I would help if I could, nothing is past. You are saying you cannot help now, and the word is doing hypothetical work, sometimes called mood, not tense work.
Some grammars describe would, could, should, and might as past forms of will, can, shall, and may. That label comes from how these words behave in reported speech, where a speaker's original words get shifted back one step: I will call becomes She said she would call. It is not true tense, since the modal itself never changes shape. The nearest mix-up is assuming that would always points to past time.
In I would help if I could, nothing is past. You are saying you cannot help now. The word is doing hypothetical work, sometimes called mood, not tense work.
There is one case where would really does stand in for will: backshift in reported speech, as in She said she would visit us that night. The reported-speech entry explains how that works, so it is worth a look if you meet would in that setting.