If you are looking for new members of staff to join your company then you will have to go through a recruiting process. Not all companies use the same methods for recruiting staff. Some choose to advertise it themselves and carry out the recruiting process in house where as others chose to outsource the recruiting to an agency. Obviously it is more costly using a recruitment agency but it can take a lot of the stress out of the process and can save time of other staff members in terms of interviewing etc.
Most recruitment agencies will vet all applicants first and even conduct a mini interview over the phone to see if they are suitable. If they feel they are, they will then contact their client and ask if they would like to invite them in for an interview.
There is no right or wrong process for job advertising it is all down to how much you want to spend and how much time you have to deal with it.