Whole Life
All One's Life, Lifelong
noun, の adjective
One life is all you get. It's your whole life. This can also mean all one's life, and when it's used as an adjective it means lifelong.
一生 is about life as a span of time: your whole life from start to finish. You'll see it in phrases like 一生の友人 (a lifelong friend) or 一生わすれない (to never forget something for the rest of one's life).
This is a jukugo word that uses on'yomi readings of the kanji. You didn't learn this reading for 生 though, so here's a mnemonic to help you:
Who has been in charge of you your whole life? The shogun (しょう).
主人は一生のパートナーです。
My husband is my partner for life.
色々自分でやらないと、一生自立できないよ。
If you don't do various things yourself, you'll go your whole life without being independent.
あなたは一生、大学一年生でいるつもりですか？
Do you intend to be a freshman in college your whole life?