Wikipedia is an encyclopedia that is mainly under free licenses, namely (as far as the text is concerned) CC BY-SA 3.0 and for the most part also the GNU Free Documentation License. Personal contributions will be published under both of these licenses, external contributions do not have to be covered by the GFDL, but in that case this must be mentioned separately.
Swedish-language Wikipedia retrieves its images from Wikimedia Commons, which itself regulates which images are acceptable. When uploading, this policy is thus not applicable. Some of the images on Commons are not copyrighted, others are under a free license. Regarding the use of images, the images on Commons are considered sufficiently free for Swedish-language Wikipedia.
Note that you may personally have other obligations than those set out in this policy, depending on where you are staying and where you are located. For example, Swedish and Finnish law provide protection for certain new photographs of old works, while some of these photographs based on judgments in the United States may be used freely in Wikipedia.
Most of the material posted on Wikipedia is protected by copyright under the Berne Convention for the Protection of Literary and Artistic Works, and is formally licensed to the public through one or more free licenses. The licenses used by Wikipedia allow free use of the content in the same sense as free software is free. Copyright licenses that, like this one, give you the freedom to use the material but not to switch to an unfree license are sometimes called copyleft as opposed to copyright. Some of the material is not subject to copyright, for example because it is old, too simple to enjoy protection or because the specific type of government agency is not covered by copyright.
Previously, Wikipedia used the GNU Free Documentation License (GNU FDL or GFDL) for the texts, but after a 2008-2009 vote, CC BY-SA was introduced as the main license. Personal contributions will be under both licenses, but for material downloaded outside of Wikipedia, it is sufficient that it is under the latter.
Exceptions to Wikipedia's free licenses
There are some exceptions to Wikipedia's free licenses, including quotes, images that are free in some countries but not others, Wikipedia and Wikimedia logos, and some of the images in other language versions.
The right to use the material may also be limited by laws that have nothing to do with copyright, for example with regard to trademarks, government symbols and images of persons.
Of course, it is also possible that an image on Commons is uploaded in violation of Commons regulations and that the license information is incorrect, even if the users of Commons make an effort to find and correct such errors. The person who reuses images must independently assess whether the information for the images used should be considered reliable.
Quotes and de minimis
Quotes can be used on Wikipedia, even though the text is protected by copyright, in accordance with the citation. This is formulated similarly in Swedish and Finnish law: the quotation must be made in accordance with "good practice" and may only be of a "scope motivated by the purpose". Good practice means, among other things, that the author must be clearly stated and that the sentence must not be distorted.
Copyrighted details can be included in images that are considered free according to the principle de minimis non curat lex (the law does not care about small things). In addition, there are explicit formulations about situations where details are not protected by copyright. In Finland, for example, works of art (which have been permanently transferred) may be included in images with other main motifs. A photograph of a square with a statue is thus allowed, but a picture of the statue may require a permit. In borderline cases, captions and other contexts can be crucial. In particular, publishing a cropped image can be illegal.