Hi. >"to start doing smthing " is "sth o hajimeru(present tense)" or "sth o hajimemasu(more polite)" or "sth o hajimeta(past tense) or "sth o hajimemashita(more polite) >"to finish doing smthing" is "sth o owaraseru or oeru"(present tense) "sth o owaraseta or oeta "(past tense) Well,it depends. "o"is postposition,usually put after the object. "ta" is usually put after the verb and change the sentense to the past tense. For example, I started to learn Japanese. watashi wa nihongo o manabi hajime mashita In hiragana, わたし は　にほんご　を　まなび　はじめ　ました。 In this case, wa and o are both postposition. But "wa"(not pronounce ha) is usually put after the subject. Uhh,it is hard for me to explain in English. I hope you understand it^^

to start:~ wo shi hajimeru / ~ wo yari hajimeru. / し始める、やり始める to finish: ~wo shi oeru / ~ wo yari oeru. / し終える、やり終える wo is a particle mainly for accusative used.