First off, let's get this straight: Strictly speaking, hash is a "dab" - but one with a much lower cannabinoids percentage than the dabs of the new generation and it is produced in a totally different manufacturing process.
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Basically, the process of producing budder or shatter or BHO or how ever you might call it, is, that buds (preferably very resinous, but high quality in general and in the first place) are stuffed into a tube and a liquid chemical solvent is allowed to drop through the tube then. One can use snippets of the plant as well, but for obvious reasons the result will have a lower cannabinoids percentage and you will end up with less budder (regarding the weight of plant matter to end-product ratio). The solvent "washes" the cannabinoids out of the plant material and eventually drips out of the tube, where it forms a liquid stream in the color of, well, urine. This liquid is collected in a glass dish (the best material to allow for easy cleaning - and to scratch the product off from) and gently warmed to remove the excessive solvent. The result is a dab. The quality of the dab depends on several circumstances, but the most important parts are the feedstock and the quality (Purity is the key! Don't be a cheapskate if you want to produce a high quality product) of the used solvent.
We are talking about producing dabs. Before you even think about it, read about it, talk to people who have done it before (successfully!) and be cautious! The involved chemicals can have fatal effects! Butane is highly combustible and careless use can cause an explosion whereas CO2 in high concentrations can cause death by suffocation. Bottom line: Get wise before you try it and stick with smoking dabs instead of making your own if you have no 100% secure setup.