This best way to increase your Korean vocabulary is to constantly ask about the Korean names or labels of objects around you. It would bl even better to ask your questions in Korean. If you can read Korean, another method of increasing your vocabulary is to ask what the particular word would be in English. Such a desire to acquire vocabulary indicates that you have great potential for learning Korean Well.
A : 이것은 한국어로 무엇입니까? / What do you call this in Korean?
[Igos-eun hangugo-ro muos-imnikka?]
B : 그것은 한국어로 사과입니다. / It is called “sagwa” in Korean.
[Geugos-eun hangugo-ro sagwa imnida.]
A : 이것은 한국어로 무엇입니까? / What is this in Korean?
[Igos-eun hangugo muos-imnikka?]
B : 그것은 한국어로도 파이애플입니다. / It is also called “pineapple” in Korean.
[Geugos-eun hangugo-rodo painaeple imnida.]
A : 파인 사과가 아니군요? / Oh, not “pinesahgwa”?
[Pain sakwa-ga anigunyo?]
B : 네? / Excuse me?