Professional choice
If you have headhunting experience, it is better to learn HR, because with real experience, you will know what to learn, how to learn and how to use yourself.
Application material
In addition to IELTS scores, you need to provide graduation certificate, degree certificate, report card, two letters of recommendation, personal resume (CV) and personal statement (PS) (the topic of each school is different), and if you have any, you can also provide proof of grade ranking.
Application procedure
Every school has different procedures, but now there are many online applications. You can submit the scanned document, enter some information and wait.
Matters needing attention
If you have enough time, you don't need to find an intermediary, and you can apply yourself. If you are busy, I suggest you find a free agent. If you go to Britain, the best one should be UKEAS, because it is run by the British Ministry of Education and has something to do with universities. The application is reliable and the whole process is very clear.