Before learning the verb tense first you need to know that there are 3 verb forms in Korean: Dictionary form, Written form, Spoken form.
The part of the word preceding 다 is called the “Verb Stem”.
ex) 읽는다, casual = to read
ex) 읽습니다, polite = to read
: Polite verbs can be also used in polite speech. For instance you’ll hear a news reporter using polite verbs in their speech.
ex) 읽어, casual = to read
ex) 읽어요, *casual polite = to read
* I differentiate polite verbs from casual polite verbs. You’re most likely familiar with 2 categories — casual and polite. However I group the verbs in 3 groups to be more specific, as there is significant differnce in politeness.
you look up a verb, 가다 (= to go) in a dictionary.
In this case, 가다 is a dictionary form. 간다 is a casual written form, 갑니다 is a polite written form, 가 is a casual spoken form, and 가요 is a casual polite form of the verb.