Airlines look for people with customer service experience, and normally require you to be at least 21, however, some smaller airlines do hire at 18 or 19.
For information about the job and which airlines are hiring, as well as requirements:
You would then go on the website of the airline, just like any other employer and apply online, uploading your resume and information.
You need patience and poise.
The job requires you to be pleasant, friendly and courteous even under stressful and difficult circumstances.
If the airline likes your resume and application you will be called for an information session in a large group. This is where they see how you look (well groomed, poised) and how you interact with others (friendly and patient).
Show up looking professional; if possible a dark suit and a white blouse or shirt, men should wear ties, and women if a skirt suit should wear hose and conservative shoes, jewelry and hairstyle.
If you don't have a suit, at least wear a conservative outfit like you would wear to work in an office. This is not the time to show off your style or to dress provocatively.
No visible tattoos or piercings other than one or two ear lobe piercings.
If you do well there, you will be invited to a group interview and then a one on one interview.
If all that is good you will be offered a job contingent on passing a 10 year background check, drug test, and physical exam.
Then you will be invited to initial training, usually several weeks, which you must pass in order to actually be hired and get your operating experience prior to flying.
In the interview they want to hear about how you can provide good customer service and provide the passengers with a positive flying experience.
They will also ask if you are willing to relocate and if you can work a very unpredictable schedule, be on call on short notice and work potentially long days.
To this you should answer yes.
They will inform you that you will be on reserve for several months to several years. This means you will be on call with no guaranteed schedule. You may have only 1 or 2 hours notice to arrive at the airport in uniform ready to leave on a trip of 1 day, or several days.
This is all true; the recruiter is not exaggerating but is giving you fair warning.
Good Luck! It is a great job for the right person