What is a constructed language or conlang?
A constructed language, planned language, or conlang is a language made up deliberately by a person or group of people rather than having evolved naturally. "Planned language" is more often used to mean a language intended for actual human use, and "conlang" is more colloquial. Language games are a kind of conlang (ex. Pig Latin). For a more detailed explanation of conlangs, head over to the Wikipedia page on conlangs.
What is a constructed script or conscript?
A constructed script or conscript is a writing system made up by a person or group of people, usually to go along with a conlang, which did not evolve naturally. A substitution cypher could be considered a kind of conscript. For a more detailed explanation of conscripts, head over to the Wikipedia page on conscripts.
NOTE: Not to be confused with conscription.
Who can conlang?
Anyone can conlang. If you want to, go ahead. If people say it's silly or pointless, you can point out notable languages such as Quenya, the elvish language by JRR Tolkien in his fictional world Middle Earth, Klingon, the language of the Klingon race in Star Trek, or Esperanto, an auxiliary language which has around ten-thousand to two-million speakers. There are many more, but these are three of the most popular and they all have people that know and speak them. Besides, if you enjoy it, why not do it if it's not hurting anyone else?
Why do people conlang?
There are many different reasons why a person might conlang: Perhaps they want to make a language for everyone in the world to learn so we all have a unified language and can communicate better (these are often called '[constructed] auxiliary languages'). Or maybe they're writing a story and want a language to go along with a group of people in the story so it seems more authentic. Maybe a group of kids want to communicate with each other but not allow pesky parents, siblings, or classmates to know what they're saying or writing. Perhaps the person just enjoys it.
How should I approach this guide?
In each section, I try to include information, options, and exercises or questions to ask yourself in order for you to create a constructed language. It is up to you as a reader to choose whether you would like to make a simple or more complex language.