I'd heard it wascame from Europe, but I didn't know the details, so I looked it up this time.

"came from Europe" is more natural for talking about this kind of import

Then I found that it was thecame from a religious story about St. Valentine in the 3rd century AD.

However, now it is (a/the) day for couples, especially in Japan.

Saying "the day" implies it's the only day or the most important day. "a day" has a little less judgement. I think in Japan there is also White Day, so this is implying that Valentine's Day is more important than White Day (I'm not Japanese, so don't know if that's true).

So, it's a very commercial event nowadays in Japan, but it might be good that femalewomen and girls have thea day to tellshare their love towith their partner.

"females" can come across as a little distant and clinical.

If you have time, it's so would be useful for me that you teach me the difference between "woman" and " female".)

Differences:

- Woman is a noun for adult female. So girls are female, but not usually considered women yet. That said, you might find a bathroom or a store labelled as a a women's clothes store or a women's bathroom and in those contexts it's understood that it covers women and girls.
- Female is both an adjective and a noun. That said, the noun female comes across very stiff so is mostly used in scientific contexts only, or when talking about animals etc. Talking about humans that way comes across a little like you don't interact with women much. Note this negative connotation only applies to using it as a noun! The adjective is more frequently used in day to day life.

I'd heard it was from Europe, but I didn't know the details, so I looked it up (this time).

It would sound more natural without “this time.”

Then I found that it was therelated to a religious story about St. Valentine in the 3rd century AD.

It is quite common in Japan thatfor a woman to gives chocolate to her boyfriend on this day.

It seems that one Japanese food company tried to hold an event that contributed to its profit in February.

This sentence appears to be grammatically correct, but I don’t understand your point. Are you saying that, in order to increase their profits, a specific Japanese company started this trend of women presenting chocolates to men on Valentine’s Day?

So, it's a very commercial event nowadays in Japan, but it might be good that females have theis day to tellexpress their love to their partner.

( Thank you for reading.

Delete the space after the parentheses mark.

If you have time, it's so would be very useful for me that youif you could teach me the difference between "woman" and " female".)

“Woman” refers only to humans. “Female” can apply to animals and some plants & flowers, in addition to humans. “Female” sounds more scientific than “woman.”

I'd heard it was from Europe, but I didn't know the details, so I looked it up this time.

Then I found that it was thea religious story about St. Valentine infrom the 3rd century AD.

However, now it is thea day for couples, especially in Japan.

It is quite common in Japan thatfor a woman to gives a chocolate to her boyfriend on this day.

So, although it's a very commercial event nowadays in Japan, but it might be good that femaleswomen have thea day to tellexpress their love to their partner.

Here, it would be more appropriate to say women, rather than females. Also, using 'although' here sounds more natural.

If you have time, it'sd be so useful for me that youif you could teach me to teach me the difference between "woman" and " female".)

'Female' is used in more biological/anatomical/medical contexts. In most regular conversations, you'd say woman. Hope that helps!

Then I found out that it was thea religious story about St. Valentine in the 3rd century AD.

ISo that means that Valentine's Day is actually related to Christianity.

However, now it is thea day for couples, especially in Japan.

It is quite common in Japan thatfor a woman to gives chocolate to her boyfriend on this day.

It seems that one think a Japanese food company tried to hold an event that contributed to its profitjust to make money in February.

I'm a bit confused by "contributed to its profit". So, apologies if my correction isn't accurate.

So, it's a very commercial event nowadays in Japan, but it might be good that femalesfor women to have thea day to tellfor showing their love tofor their partner.

"Female" feels weird here, explained below.

If you have time, it's sod be really useful for me that youif you could teach me the difference between "woman" and " female".)

"Female" is exclusively biological. To me, it feels a bit awkward when used to refer to people outside of a medical context. It might even be a little offensive in some regions of the United States. "Woman" (plural: "women") has a less scientific tone, and is far more commonly said in everyday life (as is "man"/"men" instead of "male"/"males").

I could also try to write about "biological sex" and "gender", but that's a long story. If you don't know anything about that and want to know more, Wikipedia explains it pretty well: https://en.wikipedia.org/wiki/Sex%E2%80%93gender_distinction