To my knowledge 'Sé' is for the subject and 'é' is for direct object in most cases. So 'Taitnionn sé é' would be 'He shines it'. You can sometimes tell if a word is masculine or feminine by the ending. Most nouns are masculine but most often nouns ending in a slender consonant, -eog, -óg, -lann, multi-syllable nouns ending in -acht or -íocht, and country and language names are feminine.
I think you use é with nouns or adjectives, and the word is (remember "is cailín í?"). If you were saying it is shining, maybe you'd use é, but taitníonn is a verb. That's my guess, based on what we've learned at least!
As for gender of a word, it seems to have to do with declension. I've gotten a bit frustrated with it myself, so I found this link, and maybe it'll help. http://nualeargais.ie/gnag/subst3.htm
Rachel, just like French and German, every noun in Irish is either masculine or feminine. That's why bean becomes an bhean after the singular definite article (feminine nouns are lenited after an in the nominative case), but fear becomes an fear (masculine nouns are not lenited after an in the nominative case).
Look up any noun in a good Irish dictionary (such as the Foclóir Gaeilge-Béarla), and the gender of the noun will be indicated at the start of the entry.
Since when? Sorry but i've been learning irish at school for 11 years, and never once has gender of words been mentioned. I thought it was weird when in secondary school we started learning french and german and they had genderised words. I just assumed irish didnt. Jeez, like not my fault I've been learning something 11 years and no teacher ever bothered to tell me this information.
I had exactly the same reaction when I encountered this idea of gendered nouns when I started using Duolingo, and I've checked with lots of other people who learned Irish in school, and many of them were also surprised. So there's nothing unusual in your experience, but the gender of nouns really does matter - it's why we say an bhean bhocht rather than an bean bocht, and why we say muintir na hÉireann rather than muintir an Éireann.
é is a pronoun.
é 3 sg. m. pron. He, him; it (usually referring to m. noun). (Has various grammatical functions, but cannot be the subject of an active verb) 1. (a) (Direct object) Déan é, do it. Chonaic mé é, I saw him, it. ......
sé, 3 sg. m. pron. He; it (usually referring to m. noun). (Subject of verb; not used with copula) 1. Tá sé go maith, he is well. Tá sé déanta, it is done. Cheannaigh sé teach, he bought a house. Chosain sé anrud airgid air, it cost him a terrible lot of money.
Given the less than stellar reputation of the Irish secondary school curriculum when it comes to the development of anything approaching basic competency in Irish, never mind fluency, it shouldn't come as a surprise to encounter unfamiliar expressions, usages and constructions.
É sin ráite, outside of ag taitneamh, it is unusual to see taitin used this way.
That's a rookie mistake. You should read the dictionary definition of taitin:
It doesn't mean "like". With the addition of the preposition le, you can translate it as the verb "please" - taitníonn sé liom - "it pleases me", which can be understood as "I enjoy it" or "I like it" but note that the subject of the Irish sentence (sé) does not match the subject of the English sentence ("I") when you swap the verb from "please" to "enjoy"/"like".
No it should not.
"It" is not a noun, it's a pronoun, just like "he". There is no difference in Irish between "he" and "it". The subject of an active verb is sé, not é, whether the sentence in English has "he" or "it" as the subject. The object of the sentence will be é, not sé, whether the English sentence uses "him" or "it" as the object.
rinne sé arís é`- "he did it again"
tá sé ag cur fearthainne - "it is raining"
leag sé amach é - "it knocked him out"
bhí sé go hiontach é a fheiceáil - "it was great to see him"
Taitníonn é is something like "him shines" - it is not grammatically correct.
Irish does not differentiate between "he" and "it" - sé can mean "he" or "it" depending on context, and é can mean "he", "him" or "it", depending on context.
That doesn't mean that you can choose between sé and é whenever you want. é can't come immediately after a verb - you have to use sé for the subject of a verb, whether the subject is "he" or "it".