I noticed that is a process on how to paint any surface, in this case a railing.
In detail the steps are:
1. Cleaning the surface to paint and then put on a tape to cover the parts you don't want to paint, maybe on the wall and floor.
2. Cleaned and covered the necessary parts, now it's ready to be painted. Meanwhile the painting has to be ready.
3.
Now the painting can be applied. If you cover enough the floor and wall the process should be faster.
4. Once applied the stain it is needed to keep away until the painting is dried. After a couple of hours the tape has to be removed.
So the steps in the right order are:
B, C, D, A
Extra comment:
As good as you prepare things at the beginning as fast as you can finish it.