それ・その details
Examples
takes up what was just said — the noun after その is the one already on the table
昨日、知らない番号から電話がきてさ。その番号、調べてみたんだ。
kinou, shiranai bangou kara denwa ga kite sa. sono bangou, shirabete mita n da.
I got a call from a number I didn't know yesterday. I looked that number up. casual
先週、山で事故があったそうです。その後、登山道は閉じられています。
senshuu, yama de jiko ga atta sou desu. sono go, tozandou wa tojirarete imasu.
I hear there was an accident on the mountain last week. The trail has been closed ever since. neutral
お問い合わせの件ですが、その後いかがでしょうか。
o toiawase no ken desu ga, sono go ikaga deshou ka.
Regarding the matter you asked about — how have things been since? formal
something only the other side has met — the speaker takes it as the listener's information, not their own
その話は、今日初めて聞きました。
sono hanashi wa, kyou hajimete kikimashita.
That's the first I've heard of it, today. neutral
そちらのご都合がよろしければ、来週お伺いいたします。
sochira no go tsugou ga yoroshikereba, raishuu o ukagai itashimasu.
If it suits you, I will call on you next week. formal
Formation
その＋名詞・それ（前に出たことがらを受ける）attaches to noun phrase (schematic)
Notes
よかったね); その・それ makes no such claim — it takes what the conversation
just supplied, or what only one of you has met.
Related patterns
Similar
そんな and その both look back, and they pick up different things — その話 is THE story just mentioned, そんな話 is a story of that KIND, so そんな can dismiss a whole class (そんな話は信じない) where その can only point at the one on the table.
Lookalikes
その is a single word that attaches straight to its noun, so the genitive の never appears with it — 私の本 needs the の between two nouns, その本 takes none, and ×それの本 is not Japanese.
Combines with
それで, それから and それに are this same そ welded to a particle, and the difference is what they pick up — その＋noun takes one thing out of the previous sentence, while the connectives take the whole sentence and carry it forward.