Introduction
What is a conlang? Why are they made? A conlang is a language that has been constructed rather than simply existing like natural languages do. A conlang, however, doesn't have to be as big as a real language because it doesn't necessarily have to be used. A conlang typically has a complete phonology and phonotactics, a largely complete grammer, and a detailed, but far from complete lexicon, unless it's very old or intended to be a universal language, or new and hasn't been developed very much. A conlang is made for a varety of reasons. Many are made simply as art, others are made as part of a conworld, a made-up world, and some are supposed to be a universal language that would be spoken by everyone to end the problem of people not being able to understand eachother.
To get started, you need to have an idea of what your conlang will be used by. It helps to have a conworld that uses the language although this is not necessary. You also need to study up on phonology, morphology, etc. The language construction kit at zompist.com has a lot ideas and tips on how to make a conlang.