As your beer ferments, it produces an excess of yeast, which, as fermentation subsides, sinks to the bottom of the fermenter taking with it, protein material and hop fragments. Depending on the yeast, this will form a hard cake. At this point, you've got a couple of choices, either leave it until it has really finished fermenting and you have a stable hydrometer reading and then bottle it by running it into bottles in which you have already put the priming sugar, or run it into a clean fermenter leaving the yeast behind. Again, there are two choices, either leave it some days in a cooler place until the beer is clear and then bottle into primed bottles, or, when it is clear, run it into a third vessel to which you add all the bottling sugars and stir very well to ensure these sugars are distributed throughout the beer and then bottle. This is called batch priming. Some brewers will leave their beer to ferment out in the first vessel and then carefully transfer it directly to the bottling bucket.
I don't know what stage you added your DME solution and I hope your stirring was sufficient.