As an additional information to Raghad's topic about tenses, I want to put this topic...
Tenses are so easy if you know the exact difference between them... :wink:
1- Present tense:
1)Simple present:
We use it when there are facts. That means something was true in the past, is true in the present, and will be true in the future.
Eg: The sun rises from the east.
We use it also when there are habitual, always, usually, everyday activities.
Eg: It snows in Alaska.
2)Present perfect:
We use it when there is an action happened or did not happen before now at an unspecified time in the past.
Eg: John has already visited London.(happened).
Ann has not eaten her lunch yet.(did not happene).
3)Present progressive:
We use it when there is an action which is in progress at the moment of speaking.
Eg:Tom is sleeping right now .
We use it also when there is an action which
began in the past, is continuing at present, and will probably end at some point in the future.
Eg:Susan is writing another book this year .
4)Present perfect progressive:
We use it when there is an action began in the past and continues to the present.
Eg: It has been raining all day, and it is still raining right now.
2- Past tense:
1)Simple past:
We use it when there is an action which began and ended at a particular time in the past.
Eg: It snowed yesterday.
2)Past perfect:
We use it when there is an action which was completed before another action or time in the past.
Eg: Tom had already eaten when his friend arrived.
*Tom's eating was completely finished before another time in the past.
3)Past progressive:
We use it when there are two actions which occurred at the same time, but one action began earlier and was in progress when the other action occurred.
Eg:He was driving fast when the accident happened .
4)Past perfect progressive:
This tense emphasizes the duration of an action that was in progress before another time or action in the past.
Eg: Marry had been studying for two hours before his friend came.
3- Future tense:
1)Simple future:
We use it when there is an action which will happen in the future.
Eg: She will come tomorrow.
2)Future progressive:
We use it when there is an action which will be in progress at a time on the future.
Eg: He will be sleeping when we arrive.
3)Future perfect:
We use it when there is an action will be completed before another time or event in the future.
Eg: I will have finished my work by five o'clock.
4)Future perfect progressive:
This tense emphasizes the duration of an action that will be in progress before another time or event on the future.
Eg: I will have been cleaning the house for two hours by seven o'clock.
Note:
We can use present continuous with the future if there is an action which always happens at the same time.
Tami
... 
Correct
