You move them into schools where they contribute to your research rate(hit 'T' in-game to get to the technology page). The more stars they have the more points they generate per turn(unfortunately I haven't found a way to see how many points a particular tech requires but the earlier ones are like 40 points or so). In general it's quicker to build more schools than try to spawn more gentlemen(especially since schools themselves spawn gentlemen) but just watch out since you take a pretty severe happiness penalty if you have too many schools.
Do note that like Zerg says Scholars cannot duel like gentlemen. The eastern factions(muslim and hindu) get scholars while the western factions get gentlemen.
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