Tip, Ahead, First, Future
noun, prefix, suffix, の adjective
Everything that happened to you previously is just the tip of the iceberg, and the important stuff is ahead of you, in your future. So make sure you put that stuff first! The original meaning of this word is the tip of something, like a pen or a finger. From that meaning, it's expanded into all sorts of meanings, like ahead, first, and future, depending on the context and where it is in the sentence. It can also mean "previous" in formal contexts (and we'll accept that meaning too, but we're not teaching it here because it's more advanced).
さき
Since this word is made up of a single kanji, it uses the kun'yomi reading. You didn't learn that reading with the kanji, so here's a mnemonic to help you: Just ahead of you are the tips of a saw and a key(さき). You have no idea what they're doing there, but both saws and keys have very sharp tips, so watch out you don't hurt yourself. Imagine yourself edging carefully past those saw and key tips. You can differentiate this from 先ず (まず) because it doesn't have any hiragana on the end.
ペンの先がつぶれた。
The tip of the pen got crushed.
お先にどうぞ。
Please go first.
この先にレストランがある。
There's a restaurant just ahead of us.
先のことはだれにも分かりません。
Nobody knows what the future holds.