The social need has so many ways to fill it and their all rewarding in their own right. In fact, one page alone can't describe all the social interactions. That's why they've been split up into three pages.
Normal interactions can be performed to any sim. Romantic interactions can't be performed to family members and family interactions can only be performed to family memvers. Now for some basic information on the relationship score.
Relationship Scores
Relationships are split up into two scores: Daily and Lifetime. Daily represents short-term relationships and is volatile. Lifetime represents long-term relationships and is not as volatile as daily. This is because only a few interactions can increase or decrease it. Both relationship types can change numbers without any influence, however the way they do so is different.
Daily Relationship
Daily relationship is an extremly volatile score. It's easy to build up but is just as easy to decrease. It can also decay over time. Every day at 4pm, each sims daily will drop by two points. This can also break friendships as they must be mutual. At that time, you may be pestered with phone calls from other sims your sim knows asking to be socialised with. If you want to keep relationship high, this should be taken as a wake-up call
Lifetime Relationship
Lifetime relationship is more stable than daily. Instead of decaying, it normalises. Three times a day, the lifetime will shift towards daily score by three. There are few interactions that raise lifetime and most of them are romantic.
Availability and Acceptance
On the other pages you may see the terms availability and acceptance. For clarity these terms are defined here. Availability refers to whether a social interaction can be initiated on a sim. Think of it as an unlockable system of sorts where increasing score gives you more interactions.
Acceptance is whether a social interaction goes right. When you initiate an interaction, certain criteria must be met for it to be accepted. This is why newly unlocked interactions may go wrong when intitated.