The rules on the eviction process are fundamentally the same for England and Wales as they both rely on the Housing act 1988 and the Civil Procedure Rules which in both cases falls under CPR 55. 
The big difference is that England has the Deregulation act, which creates more hoops to jump through before you can serve a section 21 notice. Wales has their own special hoops which comes under the Housing Act Wales 2014.
For both England and Wales the section 21 does the same same thing, the difference is what  makes a notice valid or invalid in addition to the 1988 Housing Act. Yes the world has already gone insane.
To understand the eviction process if it's England refer to the 1988 Housing act and the Deregulation Act.
If its Wales it's the 1988 Housing act and the Housing Act wales. It's not confusing because there is nothing either which contradicts the core rules of the 1988 Housing act and CPR 55.
To understand the eviction process a bit more go to Accelerated possession where ever you are.