Type 'writers wanted' in your search engine and just see what pops up! Everything from jobs for writers to writing contests. Not all of these sites are legit or have legitimate information for you. Be wary of those that you don't recognize or at the very least don't even have contact information on their website. You really shouldn't have to pay up front for information about any jobs either. Some sites that offer to link writers with employers charge a fee only when the connection is made.
Another group that will advertise 'writer needed' are anthologies. Some run contests and the winning prize is a spot in their anthology, but you have to pay for the entry and then the copy of the anthology. If it is a legitimate request for a writing position they will offer to pay you for your work. If they can't pay they will offer other incentives or make it very clear that the job is not going to pay you a fee or salary.
Some sites will list many writer wanted opportunities on their website and make it easy to contact the person or company posting. Some sites are looking for writers who will work for free, such as non-profit organizations. If you are just starting out this might be a good place to begin. It will get you the experience and exposure you need while also making your work available to those who are looking for writers that want to be paid.
Some sites are set up specifically for those looking for writers. You can post your resume on these sites and people who want writers will contact you if they are interested. Some people are looking for education writers, ghost writers, speech writers-you name it. Try to have samples of all the work you can do ready to send to someone who asks for them. Even if they have never been published you can write up examples of things you know you can do. Sometimes they will not accept attachments but instead want a URL. If it is a published work (this is where writing for free can be a benefit) you will provide that. If you have a web site or blog then provide that URL.