I recently came across a project that taught me how to create a sub-domain and install wordpress on the sub-domain. It was a great experience where I had to do some research because it was something I was learning for the first time.
At this time all I had was an objective which was creating a sub-domain for the client and the rest was up to just doing research and delivering the work based on the objective.
Before we begin with there are a couple of assumptions I am making in this article
1. Your using Digital Ocean as your VPS Service provider
2. Your having Apache Server Running