léim is a noun meaning "a jump" or "a leap", and it's also a verb meaning "jump" or "leap".
But the Irish for the verb "read" is léigh, and in the present tense that becomes léann ..., and the first person singular uses the synthetic form léim:
léim - "I read"
léann tú - "You read"
léann sé - "He reads"
léann sí - "She reads"
léimid - "We read"
léann sibh - "You read"
léann siad - "They read"
léim mé - "I jumped" (past tense)
léim tú - "You jumped" (past tense)
léimim - "I jump" (present tense)
léimeann tú - "You jump" (present tense)
Yes, but how is one to know that "bris-" is first and "bail-" is second upon first learning the word? Infinitives are not given here (if that helps one determine????), and, technically, BOTH of those stems are monosyllabic, the the statements that first conjugation is monosyllabic and second conjugation is polysyllabic still doesn't help.
What do you mean by "upon first learning the word"? You either learn the word root first (bris is mono-syllabic, bailigh is multi-syllabic), or you encounter a conjugated form - (briseann is obviously 1st conjugation, bailíonn is obviously 2nd conjugation). You will never encounter bail- on it's own as a verb, because bail isn't a verb.