Adding soil

Mrs T said, among other things, that it would be a good idea to add some topsoil in the flowerbeds and put in some spring fertilizer. On Saturday, then, we bought a bag of soil and another of fertilizer--I mean, how hard could it be?

Ahahaha yeah right. Do I take the old bits of plants off first or leave them to enrich the soil? Do I remove old soil? How do I put the new soil on, can I just dump it on top or do I carefully apply small handfuls and tamp it down? Do I put it all around the plant, right up to the stems, or, um, not? How far out should it reach? How deep?

My plants are f-ed.

I didn't even get to the fertilizer. Should I have put that in first, or at the same time, or on top?

Honestly, it's like learning to cook without knowing how to boil water.