The verb in a sentence indicates what action is taking place.To inform the audience about when that action took place, is taking place or will take place, verbs have tenses. There are three main tenses: past, present and future. Each of these tenses can be sub-divided into three forms: simple, continuous and perfect.
The present tense:
The simple present tense – actions which happen regularly.
The present continuous tense – actions which are taking place now.
The present perfect tense – actions are at this moment just completed.
(Every day) I climb up the wall.
I am (currently) climbing up the wall.
I have (just) climbed up the wall.
The past tense.
The simple past tense – action which took place at a specific time and is completed.
The past continuous tense – actions that took place over a period of time.
The past perfect tense- actions that were completed by a specific time in the past.
I climbed up the wall.
I was climbing up the wall.
I had climbed up the wall.
The future tense
The simple future tense- actions which will take place in the future.
The future continuous tense- actions which will take placeover a period of time in the future.
The future perfect tense – actions which will be completed by a specific point in the future.
I will climb up the wall.
I will be climbing up the wall.
I will have climbed up the wall.