さ is a 感動詞（かんどうし） (interjection) in Japanese that has three primary uses. These are as follows:
誘（さそ）い、促（うなが）し - To invite, incite, or draw attention to something.
驚（おどろ）き、当惑（とうわく）し - The express surprise, confusion, or bewilderment.
話（はなし）の流（なが）れを抑（おさ）える - To control or keep in check the flow of a conversation.
In this lesson, we will be focusing on the second meaning (to express surprise, confusion, or bewilderment). In English, this is used in a very similar way to ‘like’, ‘you know’, ‘uhh’, and other short phrases that are employed when a speaker is searching for the right thing to say, and is filling the silence. This さ may be used in any position within a sentence, simply to create thinking time.

• あのさ、私（わたし）さあ、この前（まえ）さあ、お金（かね）貸（か）したじゃん？あれさあ、返（かえ）してくれない？
  Hey, um…. I, uhh, lent you, like, money before, right? You know… can you give that back to me?
• ね～聞（き）いてよ。彼女（かのじょ）がさ、急（きゅう）に別（わか）れたいっていって来（き）たんだけどどうすればいいの。
  Heyyy, listen to this. You know my girlfriend? She suddenly came to me saying that she wants to break up with me, what should I do.

The ‘confusion’ that this さ expresses is not necessarily a bad thing, and is used by many people to simply express that they have not finished talking yet.

• 来週（らいしゅう）箱根（はこね）に行（い）くんだけどさ…どこか美味（おい）しいところ知（し）らない？
  I am going to Hakone next week, soooo… Do you know any good restaurants?
• 夜中（よなか）に急（きゅう）に娘（むすめ）から電話（でんわ）が来（き）てさあ...本当（ほんとう）にビックリしたよ。
  You know, my daughter suddenly called me in the middle of the night, and… I was really worried.