First of all, ing is the progressive aspect of the present participle or verb. The present participle can be used as an adjective to indicate an ongoing state, such as "running water". "In progress" also means the verb progressive aspect, such as "I am typing now".
Secondly, ing can also express the form of gerund, which is often used as subject, object or preposition. For example, "Doing exercise is good for health". In this example, playing, as a gerund form, is used as the subject to express an action, that is, "movement".
Ing can also indicate the duration or continuous state of progress. For example, "I've been waiting for you", where "waiting" refers to the duration of an action, that is, "I've been waiting". In this usage, ing is usually used with auxiliary verbs such as have, as and had.