|You might not.|
If your text is simple and it doesn't matter if some words are "slightly off" or even wacky - and you just want to have an idea of what it says, you can use any number of free online services. Google Translate will let you cut and paste text into a search box, other sites such as linguee.com are also very good but they restrict you to a couple of words, dict.cc is also mostly for single word or phrase translations.
You might find a language student or language teacher who will take on a translation for a nominal fee. Or a relative. Maybe even for free. But then, you can't complain if the quality is sub-par or if you receive the translation a month later than you actually needed it.
The above-mentioned avenues are all very risky if you need a contract, website or annual report translated, to name a few examples, by a fixed deadline.
Even if you speak both languages,that is, the source text language (the language of the text you want translated) and the target text language (the language you want the text translated into), you might not be comfortable with the specific terminology involved, or have the time to take on a translation project yourself.
At this point, I'd say it is time to look around for a translator. Usually,although not always, you will get the best results from someone for whom the target language is their native language. For anything that is even mildly complicated, it is a good idea to find someone who worked in the specific field, has a degree in that subject, or at least some level of expertise in the area. In some cases, you might also want to look for someone who has worked in the countries where the two languages are spoken as a first language.
If you need the text translated into multiple languages (a website that needs to be localized into many languages), you will either have to work with a team of freelance translators that you "hand pick" or you will need to select a translation agency, who will do this for you. Some freelance translators can assemble a customized group of multi-lingual translators for your project and will manage the project for you.
Also, if the project is large (100,000 words with a one week deadline would qualify here), you will either have to find a freelancer to organize a team for you, build the team yourself, or have an agency build a team. Each scenario has its own "pros" and "cons" with regard to cost, how much control you will have and how much of your time this will take.
Projects that involve several hundred, several thousand or even tens of thousands of words can easily be handled by a single freelance translator, depending on the subject matter and the deadline involved. Even the aforementioned 100k translation project can be handled by a freelancer, assuming the deadline is reasonable.
Many freelancers have their own websites. Tooting my own horn: www.carolmueller.com and www.translategerman.com are my 'calling cards'.
Freelance translators' websites can be found by entering keywords, such as German to English financial translator or Spanish to Dutch medical translator, into your preferred search engine.
There are also directories (some more formal, some less formal) of freelance translators. Many are searchable, meaning you can find a translator for whom English is the mother tongue, who lives in United States, has a medical degree he/she obtained in Denmark, has practiced medicine there (and possibly here as well), is retired from the profession and is now offering Danish to English medical translations. Many directories also let you enter geographical preferences.
One such directory:
More to follow soon...