Biachlár- literally food board, Bia-food, Bialann-dining room, Boardbia- Irish food board,
Chlár-board, Chlárdubh- black board- classic from primary scoil, But now we used an chlár bàn!
Hope this helps or at least wets the appetite!
(bear in mind I'm not a native speaker so any mistakes I make please correct)
You only add a séimhiú (that's what that "h" is called in Irish) to feminine nouns after an (in the nominative case).
bean is a feminine noun, so you get an bhean.
Biachlár is a masculine noun, so you get an biachlár.
Bialann is a feminine noun, so you get an bhialann.
The gender of a word is not determined by the vowel that comes after the first letter (though the ending of the word does give some indication of what the gender is likely to be).
The first example of lenition that you will encounter here on Duolingo is that feminine nouns in the nominative case are lenited after the singular definite article an - an bhean, an phéitseog, etc. The Tips & Notes describe 6 other common causes of lenition.
The first example of eclipsis that you encounter on Duolingo is probably preposition + an - ag an mbean, ar an bpéitseog, etc. The Tips & Notes describe 3 other common causes of eclipsis.
Irish, like English, doesn't have a formal "you". Unlike English, Irish does have singular "you" (tú) and plural "you" (sibh), giving rise to the singular prepositional pronoun forms agat, ort, leat, duit, romhat etc, and plural agaibh, oraibh, libh, daoibh, romhaibh, etc.