Some businesses still put up "Now Hiring" signs, but the internet is probably the most popular place for employers to advertise new job openings. Hiring officials may place a job posting on a career search website, the company website, or both. These postings should include the job description, requirements, any salary information that they choose to share, and directions for applying.
There are a number of websites that are specifically designed to connect applicants with job openings. Many companies will place their employment opportunities on these websites as a way to reach more people looking for work. A quick internet search will point you to some of the bigger ones. Be sure to confirm it is a legitimate site before entering any of your personal information!
You can also find open positions by identifying local companies and small businesses where you might like to work and then checking their company websites for postings. You might have learned about these companies through word of mouth conversations, through searching online, or through local organizations that help people find jobs, but once you know that they are great places to work, you can bookmark their websites in your browser and check for new postings regularly. Often, there is a "Careers" or "Employment" link on the main page, but this information also might be tucked under another heading, for example, "News" or "About Us." If it is listed on the main page, you will likely find it at the bottom of the web site.
Another way one can enter the job market is through a staffing agency. Many successful companies choose to hire people temporarily through a staffing agency and then, if the person turns out to be a good fit, they hire them permanently.