The process of removing oil from seeds depends in part on the nature of the activity. The word for extracting oil from seeds is "dehulling," and the machines used in the process are "dehullers." When extracting oil from some types of seeds, a press is used to crush the seed, thereby allowing the oils to seep out and be collected. Oilseed presses are commonly used in the manufacture of olive oil, for example. Processes are developed for removing the seed fragments from the oils, usually using strainers with special coatings to minimize friction.
With respect to "who" performs this task, again, the answer is dependent upon whether one if referring to a primitive society where crude hand tools are used, or a modern manufacturing and processing facility in which machines are used in the extraction process. In the former case, any member of the community had be involved; in the latter, trained employees would operate the presses. Oils intended for medicinal uses might be processed by pharmaceutical companies using very advanced equipment. Oils intended for use in subsistence living, again, involve individuals cracking open shells and extracting the content.