Ganar as a verb does mean "win" or "earn" as you've been told, but as a noun (la gana or, more frequently in Spain, las ganas) means something very similar to desire. "Tengo ganas de comer" (tener + ganas+ de) is not very strong, i'ts like "I want to..." but "Deseo verte esta tarde" - "I look forward to seeing you this evening". It is a bit stronger, like expressing a strong desire. If you just want to tell people you want this or that, use "quiero" or "tengo ganas de". "Deseo" is usually used for wishes or in a formal context. Hope that helped!

Ganar= to earn, to win Desear= to wish, to desire

In Mexican spanish ganar is like a desire too! is like "tengo ganas de ti" "tengo ganas de una cerveza" Cheers