You can apply for security jobs either through a generic job search/application website, such as Indeed.com, or by visiting the websites of the companies with security job openings. Since opportunities at individual companies depend on openings, such searches do not yield the number of results of a generic search engine.
To find security jobs to apply for on Indeed.com, enter "security" in the search engine (or a more specific set of terms, such as "security officer"). Indeed.com then brings up a list of available security jobs in the United States. You can limit search results to a particular area by entering a state, city or ZIP code into the website's search engine. Indeed.com also provides other means of defining search limits, including by salary amount, radius mileage from chosen city, job title, job type (for example, whether part-time or full-time) and by employer or recruiter.
After the website brings up the list of openings, you have two ways to apply. Some entries allow you to apply through Indeed.com, while others entries link to the company websites where you then follow the steps to complete the applications as outlined therein.
You can also visit company websites to look for openings. For example, as of July 2015, the New England Baptist Hospital had an opening for Security Analyst.