Knowing a language means many different things which can be assessed in different ways. If you already know a bit of the language you want to learn, you will want to find out what your level is. This is where a language test can tell you what you know and can do. It can probe your knowledge about the language itself (structure, vocabulary, history) or it can assess your ability to communicate in that language in more or less authentic situations. Most language tests are divided into four skills: speaking, listening, reading and writing. There are also separate tests for grammar and vocabulary. Others will help you assess your fluency, grammatical accuracy, and complexity of expressions, style, pronunciation and many other features.
Levels are often categorised into beginners, intermediate, or advanced. The meaning of such words varies, depending on the context.
