Normal vs. abnormal is like comparing apples and oranges, but also like comparing apples and say....light bulbs. It's all relative, and there are many varying shades and degrees of extremism.
Context is important to keep in mind when defining "normal"- to relieve oneself in the bushes is de rigeur in 3rd world/developing nations, but quite irregular at Buckingham Palace. This gives rise to "when in Rome, do as the Romans do" as a social epithet.
As such, what passes for "normal" within a specific circumstance can be more applicably thought of as what passes for "acceptable" in the majority of the immediate social dynamic. When you consider that less than 90 years ago it was legal to purchase cocaine in a pharmacy but you would pull jail time for having a beer, it sort of puts it in perspective.
normal and abnormal is simply a persons views, mostly influenced by modern society and peer pressure. There is no such thing as normal nor abnormal, nobody in the world is normal we are all different, its simply a persons personal view on a topic/thing.
People try to identify themselves by being normal or abnormal. This is fine. However, one might reach one's greatest potential by simply being "your best", rather than trying to fit into, or work against, statistics.
So, to answer your question, the concept of "normalcy" provides a guideline for a person's thoughts, emotions, and actions.