Social skills are really just the way we use language to interact with other people. It can involve the words we choose, the tone of voice and way we say them, the body language we use with words or instead of words, and more. Social language use is called Pragmatics. You can read some more about pragmatics here. Children who have not mastered the rules of social language use and do not acquire them through natural language acquisition may have a pragmatic language disorder. Adults can have this too, usually after a brain injury or stroke.
In my pragmatic language therapy groups, we talk about social rules in terms of expected vs. unexpected behaviors.
When we say and do the "expected" things that follow the social rules, people have NICE thoughts toward us.
Sometimes we have to be "social detectives" to look for body language clues that tell us how someone is feeling or what they are thinking if they don't tell us with their words. What are their eyebrows doing? Which way is their body facing? What are they doing with their arms? These are nonverbal language cues that communicate meaning to us...if we know the rules of what they mean!
ASHA - About Social Language Use
ASHA's Pragmatic Language Tips
Super Duper's Handy Handout - Parents Help to Encourage Social Success at Home, Too!
UCLA PEERS® Clinic Video Modeling
University of California Riverside Social Skills Resources for Children
Edutopia - A Parent's Resource Guide to Social and Emotional Learning
Please note, the information on this site is by no means exhaustive or fully comprehensive! These are just a few tips and resources to help you along the way. For more information, please speak to your child's speech-language pathologist or other related professional.