私が乗り込むやいなや、汽車は動き出した。

I had barely got aboard when the train began to move.

私(わたし)が乗(の)り込(こ)むやいなや、汽車(きしゃ)は動(うご)き出(だ)した。

Watashi ga norikomu yainaya, kisha wa ugokidashita.

私 (わたし、わたくし)

I; me; private affairs; personal matter; secrecy; selfishness

が (が)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

乗り込む (のりこむ)

to board; to embark on; to get into (a car); to man (a ship); to help (someone) into; to march into; to enter

や否や (やいなや)

the minute (that) ...; no sooner than ...; whether or not

汽車 (きしゃ)

train (sometimes specifically a steam train)

は (は)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

動き出す (うごきだす)

to come alive; to get going; to start to move

Readings: シ、わたくし、わたし

Meanings: private, I, me

Readings: ジョウ、ショウ、の.る、 -の.り、の.せる

Meanings: ride, power, multiplication, record, counter for vehicles, board, mount, join

Readings: -こ.む、こ.む、こ.み、 -こ.み、こ.める

Meanings: crowded, mixture, in bulk, included, (kokuji)

Reading: キ

Meanings: vapor, steam

Readings: シャ、くるま

Meaning: car

Readings: ドウ、うご.く、うご.かす

Meanings: move, motion, change, confusion, shift, shake

Readings: シュツ、スイ、で.る、 -で、だ.す、 -だ.す、い.でる、い.だす

Meanings: exit, leave, go out, come out, put out, protrude