少年ははしごをつかみ、登りはじめた。

boy; juvenile; young boy; youth; lad

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

ladder; stairs; going to several places in succession (e.g. barhopping)

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to seize; to catch; to grasp; to grip; to grab; to hold; to catch hold of; to lay one's hands on; to clutch; to understand; to grasp; to comprehend

to ascend; to go up; to climb; to ascend (as a natural process, e.g. the sun); to rise; to go to (the capital); to be promoted; to add up to; to advance (in price); to swim up (a river); to sail up; to come up (on the agenda)