Once upon a time, this was done by hand and the scalpel made a clicking sound as it cut into and popped out of the leather – so the people who cut out leather are still called “clickers”.
Clicking is still done by hand for prototypes and for bespoke shoes, but in production, shoe sections are cut out by accurate and especially-manufactured “die” – like pastry cutters. This ensures consistency and speeds things up. Nowadays clicking is mostly done by a die-cutting machine, in the interests of speed and repeatability. The image on the right shows a nice old one from 1922. Even with a machine, the clicker still has to choose how to line up the die and the leather to get the best results, with stretchiness in the right direction and minimal waste.
Clicking is still a highly-skilled task, requiring good judgement and lots of experience. The use of a die means that, in principle, every shoe design needs a custom die for every component, for every size. Die are expensive. However, some shoe designs, for example the Loake Beaufort , allow the same die for (say) the wingtip to be used for several sizes. It’s not hard to see how the long, elegant sweep of the extended toecap that forms the wingtip could be the same for a small range of sizes. At some point, however, this will affect the look of the shoe, so a larger or smaller wingtip die will be needed to keep the design looking as it should. At the end of the clicking process, we have the upper components of a shoe in kit form!