How a business finds people and gets them useful. The internal-or-external choice has consequences well beyond the vacancy.
Internal recruitment — promoting or moving someone already employed. Cheaper, faster, lower risk because you know them, and motivating because it shows progression exists. It leaves a vacancy elsewhere and brings in no new thinking.
External recruitment — hiring from outside. Brings new skills and perspective and a wider field. Costs more, takes longer, carries more risk, and can demotivate people who wanted the job.
The usual documents are a job description (what the role involves) and a person specification (what the person needs to be able to do).
Induction — settling a new starter in. On-the-job — learning while doing, cheap and immediately relevant, and it transmits bad habits as readily as good ones. Off-the-job — courses and qualifications away from the workplace, broader and more expensive, and it makes the person more attractive to other employers.
The objection that trained people leave is real. The alternative — untrained people who stay — is worse.
Recommend one route and justify it from the case — the skills needed, the cost, the effect on existing staff.