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EL5: Russian names

When reading Dostoevsky and Tolstoy, I find myself constantly confused with the seemingly triple names for characters. I think I've gathered that the surname is a play on the name of the father, with Fydorovich meaning "son of fydor" but what about the first names? How does Alexy become Aloysha?
gpt
First names:  Given to the child by the parents, as in the West.  Every first name has a whole bunch of nicknames traditionally associated with it.  Sometimes these are pretty random (the way "Dick" doesn't actually sound very much like "Richard") but a lot of them are made by adding an ending like "-enka" or "-ushka."  This sounds affectionate in Russian, like "Tommy" or "Sammy" sounds affectionate in English.

Patronymics:  These come second.  It's the person's father's first name plus "-ich" (for a man) or either "-vna" or "-chna" (for a woman).

Surnames:  These work the same as Western surnames, passed down from father to children.

Calling somebody by a nickname is intimate; calling somebody Firstname Patronymic is normal, and can be anywhere from friendly to cold; calling somebody Mr. Surname is formal.