Verb Aspect: Perfective vs. Imperfective

 Aspect is often confused with the closely-related concept of tense.

While tense relates the time of a situation to some other time (usually the time of speaking), aspect conveys other temporal information, such as duration, completion, or frequency.

Tense --> temporally WHEN

Aspect --> temporally HOW

Both English and Russian are characterized by  the category of aspect. But this category of two languages is quite different. In English the category of aspect shows the character of an action. That is whether the action is shown as a fact or is shown in its progress in its development. In Russian the aspect expresses the completeness (perfective) or incompleteness (perfective) of an action. 

Since the meaning of the perfective aspect -"completed action" - is incompatible with the present-tense meaning of an action "in progress at the present moment.", perfective verbs have only the past and future tense.Verbs of the imperfective aspect have the three tenses: present, past, and future. That's why the problem of choosing the correct aspect exists only for past and future tenses.

Feel free to post your questions about choosing correct aspect to this thread.=)

The more I learn about aspects, the more I realise how simple it is. This page explains things from a different angle to what I have read in the past: http://www.auburn.edu/~mitrege/russian/tutorials/0021.html

Just thinking about it as " A|->B->B->B->B->B->B->|C" where "A" and "C" are the instantaneous parts of the action (A = the start and C = the end), it makes things much clearer.