Merfolk culture isn't exactly complicated.
Merfolk learn to hunt with both their claws and spears. Merfolk childeren are not only raised by its parents, but by the entire tribe. Every female merfolk is as a mother, and every male merfolk is as a father to the child. Sometimes this leads to confusion, because it becomes unclear who is the real father or mother of a specific child.
As a merfolk ages, they are given a sort of tutelage. This tutelage consists of all the necessary skills to live in the harsh aquatic environment. They learn to hunt, communicate in their language and a set of other useful skills for survival. A merfolk is officially adult if she loses her virginity. This may sound strange to other cultures, but the merfolk see it as a sign that the now adult merfolk is responsible enough to conceive children of her own.
Habitat
As far as people know merfolks live under the water surface. They mostly live in caverns located rather deep below the water surface where the average temperature is lower and the risk of fishnets is far lower. They also have a single city like communal living place, witch suggest a level of sophistication far beyond regular animals. Their culture may not be as sophisticated as some other cultures, but they do have their own religion and way of life.
Language
Merfolks have no written language, only a language that is a combination of verbal and non verbal components, not quite unlike trolls. They communicate trough sign language, movements and a small amount of clicking noises made with their tongue. This noise is typical for merfolks as it requires a long time to master the different tones and meanings of this seemingly simple sound. This has resulted in limited communication with other races.
Merfolks communicate similar in day to day activities as land dwelling races do, their language is just far more difficult to master. Their language is adequate to express love, pain and other complex notions, and usually is combined with a lot of emotion and touching.
The difficulty in learning the merfolk language is in the many slight variations in pronunciations. If one would pronounce the same word slightly different the complete meaning of the word might change.
Note that names are a relatively strange and new concept for merfolk. When venturing on land and learning land based language merfolk do tend to pick names for themselves, either based on the names they often hear from the races they interact with, or names that have to do with the water they first emerged from.
Diet
They hunt for meat and gather the vegetation in the seas but are also known to venture on small islands to look for dates and coconuts. Merfolk that live close to settlements of oher races try to trade with them for varieties in food supply.