Hey Julian! Glad you had some success with the cinder block!
All of this knife and sharpening stuff can seem really complicated and confusing but it seems like you're excited and catch on quickly (attitude and mindset is always more important the knowledge and raw skill).
When I first started sharpening, it made it easier for me to think of it as kind of 2 stages.
STAGE 1:
The first stage is actually grinding / removing significant amounts of metal. This is what most people think of when they think "sharpening." If your blade is very dull, chipped, damaged, or too thick, you need to start with something very coarse (like a cinder block) and actually GRIND away and re-shape the metal. When you use a very coarse stone, it makes your work faster, and you can still make an edge that will cut pretty well (as you discovered) but the problem is that the coarse stone will leave deep scratch marks and the edge will be VERY toothy (rough). Also, the edge will have a burr along it's length. A burr is basically some of the old, scratched, ground metal shavings that you have removed from the side of the edge, but have not yet completely broken off. The burr maybe very sharp, but it's also very weak and will bend and flop around as you use the knife and will make the edge feel dull long before it actually is.
SO,
As you move from coarser to finer stones (like going from a cinder block down to brick, and then maybe to some sandpaper or a 1000-2000grit stone) the scratches will get smaller and smaller and burr will as well.
Once you are done with all of the sharpening / grinding on stones, you can remove the last little bit of the burr a few different ways. One method is to lightly drag the edge over / cut into a piece of wood (like you saw Murray Carter do in that video). You can think of it as scraping the last little bit of suck on "dirty" metal shavings off the the edge. You may even see a dark grey line in the wood where it pulled off the burr.
STAGE 2:
This is what you do either AFTER you are all done with stage 1 or if you have a knife that is pretty sharp, but you have used for a little while (maybe 1-3 meals) and you can feel that it's not quite as sharp as it was, so you want to just quickly tune it up without having to get out the stones and actually GRIND away more metal.
This is where you use something like leather (the back of an old belt), cardboard, or newspaper or phone-book paper. These things may seem soft, but they all have microscopic particles in them that will polish metal. Some people used fancy leather with special types of fine abrasives mixed into it's surface. However, in the "free" price-range I find that cardboard works the fastest/best on soft metals.
What you're doing in this stage is called "stropping": you will hold the blade at the same or slightly lower angle as with which you sharpened and drag the blade in the direction of the spine (this is called and edge trailing stroke as opposed to edge leading).
Stropping does a few things:
-it polishes the metal and helps to refine the little teeth along the edge of the blade
-it helps to straighten and realign the edge (as you use a knife, the thing that makes it feel dull is actually the edge getting "rolled over" and bent out of shape, not the metal actually getting worn flat; stropping helps the edge "stand up straight" again and fell sharp.)
What you will find is that if you regularly strop your knife, you can keep the edge well-maintained and go a LOOONG time (months) before the edge actually wears down to the point that stropping no longer works and you need to bust out the stones and go back to stage 1.
You can find tons of videos of sharping and stropping using all kinds of different motions and methods. This may make you wonder (as it did me) "WELL, WHAT THEY HECK IS THE BEST METHOD?" - the simple answer is the "THE ONE THAT WORKS BEST FOR YOU!" every one is different with the way that their bodies move when sharpening and what feels easiest / most comfortable to them. People are also different in what kind of edge they like on their knives (how fine, what angle, how toothy vs polished). So just have fun, experiment, ask questions, read and watch stuff online, but realize that at the end of the day, you just have to figure out what works best for YOU and what YOU like most.
Enjoy the journey and keep us all posted on your progress (and don't forget the gift certificates when you open your first restaurant
).