There are different ways to make your research paper or article open access.
Gold OA (journals)
In gold OA the publishers make the paper or article immediately and freely available from the point of publication, and usually apply an article processing charge. The APC can be costly.
Green OA (self-archiving)
Green OA involves making a copy of paper or article, usually the final draft, openly available in an institutional repository, for example Theseus. Publishers stipulate which version of the paper or article can be deposited and specify an embargo period following publication before the paper can be made open access.
Hybrid OA refers to subscription journals that charge an extra fee to make a specific article open access while the remainder of the journal remains behind a paywall.
Self-archiving is a form of free accessibility, where a publication published through a publication channel is also made freely accessible in a university's institutional repository. Most universities and research institutes have digital archives. The National Library maintains Theseus (publications of universities of applied sciences) and Doria (publications of Finnish universities).
Research institutes and funding agencies also recommend or even require that research results are made freely accessible to promote research transparency, the possibility of repetition and thus increasing reliability. For example, the Academy of Finland requires that the research they fund as far as possible should be self-archived in freely accessible archives or databases.
Self-archiving is free for the researcher and the organization, and it meets the recommendations for accessibility, visibility, and archiving in the same way as publishing in an open access journal. ROARMAP is a registry charting open access mandates and policies adopted by universities, research institutions and research funders. The Directory of Open Access Repositories, OpenDOAR, offers a list of open publication archives, among others arXiv.org.
In SHERPA/RoMEO you can check scientific journals' and publishers' copyright policies and approach to self-archiving. The service is maintained by Nottingham University. Publishers' and magazines' position on self-archiving is shown with colour codes
ROMEO colour - Archiving policy
green - can archive pre-print and post-print or publisher's version/PDF
blue - can archive post-print (i.e. final draft post-refereeing) or publisher's version/PDF
yellow - can archive pre-print (i.e. pre-refereeing)
white - archiving not formally supported
APC (article processing charge)
An APC is a fee paid to the publisher to make an article free at point of access (Gold OA or Hybrid OA).
Double-dipping describes the situation where a journal charges an APC on top of its normal subscription fee if an author wishes to make their particular article OA. In effect, the institution is paying twice. (Hybrid OA)
A period of time defined by the publisher during which the author can not publish a self-archived open access copy of the publication in question. Embargo periods are typically from 6-36 months. The embargo period starts from the date of publication.
Final published version/Publisher PDF
The paper or article in the format in which it appears in the publication (i.e., the final version with the proper layout).
A university's or research facility's online database of their OA works. Repositories do not undertake peer review but do hold material that has been peer reviewed elsewhere. In addition repositories can hold 'grey literature' such as Theses, Discussion Papers, Datasets and other material for example Theseus.
The paper or article is published in a journal by a publisher, but a copy (usually the final draft) is made available OA in a repository. (Green OA)
Post-print/Final draft/Author accepted manuscript
A paper or article that has been peer-reviewed and accepted for publication but hasn't yet been laid out for publication by the publisher.
A draft version of a paper or article that hasn't been peer reviewed.