"Maketh" is an old grammatical form in English that is no longer used. I think it is just the third person, used both in singular or plural. In this case it means "Manners make the man," which in turn means "good manners are the most important characteristic of an upper-class gentleman (=caballero? hidalgo? señor?)
"Maketh" was still current at the time when Shakespeare wrote, and also when the famous King James translation of the Bible was made, in 1611. Literature and poetry from that era use it. The King James version is a landmark of English-speaking culture and literature. It is the English counterpart to the Reina-Valera in Spanish. Words ending in -eth are thus familiar to many modern speakers. It can sometimes be used to make something sound weighty or important.
In the King James version, the famous Psalm 23 (Salmo 23) begins:
"The Lord is my shepherd; I shall not want. He maketh me to lie down in green pastures: he leadeth me beside the still waters. He restoreth my soul: he leadeth me in the paths of righteousness for his name's sake."
The same verse, in modern translation, reads:
"The Lord is my shepherd, I shall not want; he makes me lie down in green pastures; he leads me beside still waters; he restores my soul. He leads me in paths of righteousness for his name’s sake."
Thus, all the -eth ending are replaced by the normal modern -s ending, and there are a few other small changes to modernize the language.