1. Articles published in Open Access journals are usually financed through publication fees (APC).
The publishing costs are usually paid by authors or their institutions.
2. Free access to individual articles from subscription-based journals can be purchased.
In the case of so-called "hybrid" Open Access, access to individual articles is purchased by authors or their institutions. Hybrid publishing is not supported by many research funding societies, such as the DFG, because of the risk of double funding through subscription costs on the one hand and publishing costs on the other.
3. Publishing articles or monographs at no cost to the authors or their institutions
Documents are published on institutional or subject-specific repositories which do not charge any fees. The required infrastructure is provided by the institutions or a scientific society.