If you are meaning what do you need to apply to be cabin crew, then it will vary by airline- for the airline i work for: 5 GSCEs minimum with English , Maths at grades A-C, plus these days with hundreds of people applying for each place, at least one foreign language is also looked for.
On top of the formal qualifications add being presentable, good spoken english (polite and not slang), and good at dealing with people, managing stressful situations, calm in a crisis.
Hope that helps.