It's all about time. Things can happen now, in the future or in the past.
The tenses simply show the time of an action or state of being as shown by a verb.
The verb ending is changed (conjugated) to show what time it is referring to.
In English we use two tenses to talk about the present and six tenses to talk about the past. There are several ways to talk about the future some of which use the present tenses, these are:
The simple tenses are used to show permanent characteristics of people and events or what happens regularly, habitually or in a single completed action.
The continuous tenses are used when talking about a particular point in time.
Sometimes you need to give just a little bit more information about an action or state...and that is where the perfect tenses come in.
The perfect tenses are used when an action or situation in the present is linked to a moment in the past. It is often used to show things that have happened up to now but aren't finished yet or to emphasize that something happened but is not true anymore. When they end determines which of them you use.
Perfect tenses are never used when we say when something happened i.e. yesterday, last year etc. but can be used when discussing the duration of something i.e. often, for, always, since etc..
The Future Tenses
Discussing the future in English can seem complicated.The present simple, present continuous, present perfect simple and the present perfect continuous can all be used and often it is possible to use more than one structure, but have the same meaning.