Social Points (SP) are a type of currency that became available after the Neighbours Update was installed. They're similar to Lifestyle Points, but are purple in colour instead.
Where to spend them
You can spend Social Points in the home store and online store. Anything that costs SP in the home store has a purple diamond like shape in the top left corner. Previously, the Nightclub costed 15 SP to build but as of the Grand Garages update (2019) you'll receive it for free when you start.
During live events, you can use SP to speed up tasks. For normal tasks you would use Lifestyle Points.
How To Earn
This is the main way to earn SP. Visiting your neighbour's town and completing tasks, in exchange you will receive 1 SP.
You may have a chance of earning SP by watching ads. This is not reliable since you can earn other items (Lifestyle Points, Furniture, Simoleons etc).
The Social Point Flower
After the completion of the Money Grows On Trees? quest, you can plant the Social Point Flower. Which costs 20 LP (previously 5) . The amount of SP varies depending on the result of your roll.
You can purchase SP in the online store for real life money. The price can vary depending on the location of the purchaser.
Once you reach VIP level 8, you can earn one free daily Social Point Flower.
Many live events contain SPs as a reward for completion.