First stage after being reached out to by the H.R. personnel is an invitation for an interview. This interview is a physical in-house interview at the office in Lekki, Lagos, Nigeria. It is a group/panel interview with various heads of departments assessing your overall performance and where best you fit if you're not big on a particular role.
Upon successful completion of the first stage, if passed, second stage is another invitation to the company asking for a "one-on-one chat" with the Managing Director of the organization. In my case, salaries were negotiated at this point but I'm not sure if that is the norm.
Third & final stage is when the company sends you an offer letter via email and makes a request for the incoming employee to confirm acceptance and tender requested documents.