Verbs are a category of words that describe an action that happens.
Unlike other type of words, they have a "time" quality. What this means is that by looking at the verb in the sentence, you can tell when the action happened. This means that the verb informs the reader if the action is being carried out NOW, has been carried out in the PAST, or will be carried out in the FUTURE.
Unfortunately, because of this, tenses can become complicated because we try to convey when it happened by changing just ONE word in the sentence.
For example:
Sports commentaries - (simple present tense)
"He passes the ball to Pele, who dribbles it past the defenders to score a GOAL! They win the game!"
Talking about the past for a completed action - (simple past tense)
"He passed the ball to Pele, who dribbled it past the defenders to score a GOAL! And that's how they won the game yesterday." (Simple past tense)
Something that happened in the past (but just only) - (present perfect tense)
"Good news! The principal has agreed to give us a half day holiday next Monday!"OR:"She is crying right now because her mother has scolded her."
Something in the past, in relation to something else that happened later in the past (sounds confusing?) - (past perfect tense)
"Bad news! The principal had agreed to give us a half day holiday but changed his mind when he heard about our bad results. The half day is off!"OR:"She cried all day yesterday because her mother had scolded her."
Something that is happening at the moment. RIGHT NOW. - (present progressive tense)
"She is crying."OR"I am working in this company."OR"They are studying in Tampines Secondary School."
Something that was ongoing in the past but was interrupted by another action, or stopped happening at a certain time - (past progressive tense)
"She was crying when her father came home."OR"I was working for the company in 2009."OR"They were studying in Tampines Secondary School before they graduated in 2009."
Something that was ongoing from the past until now. - (present perfect progressive tense)
"She has been crying a lot recently."OR"I have been working for this company for the past two years." (working for 2 years up till now.)OR"They have been studying in Tampines Secondary School since 2009." (studying from 2009 up till now)
Something that started in the past and continued for a duration up till another time in the past. - (Past perfect progressive)
"She had been crying when her father came home." (Similar to past progressive tense; however, notice that a duration is specified for PPP tense.)OR"I had been working for this company for 2 years when it went bankrupt in 2009."OR"They had been studying in Tampines Secondary School for 2 years when it underwent renovation."
Using the correct tense will unfortunately take a lot of time and practice - however, over repeated use, it will become natural, and you will not have to think about which tense to use.

