What is the difference between Perfective and Imperfective verbs?

Words in Russian language have very expressive morphology – that is their certain parts add to the meaning. For example, the word читать is different from прочитать, although they both have to do with reading. The first one is Imperfective aspect, and the second is Perfective. To put it more simple, Imperfective describes the process. Я буду читать книгу (I will be reading a book) indicates the ongoing action with unknown result. I will be reading it for some time, it is the process that I am interested in. It can also be a habitual action: я читаю книгу каждый день (I read a book every day).

Now if you say я прочитаю книгу (I will read a book), you are interested in a result. You indicate that you are committed to finish it.

The verbs in Perfective aspects usually have prefixes that are missing in Imperfective. For example, it will be выпить – to drink (Perfective) as opposed to пить (Imperfective), сделать – to do (Perfective) and делать (Imperfective).

The most common prefixes would be

Про, по, с, на, вы, при.

However, there are few exceptions, as some verbs change their form completely. For example, the verb to take is брать in Imperfective and взять in Perfective. 

In addition to that, some verbs have different suffixes as opposed to prefixes - parts of the word closer to an end. For example, it is решать - to decide (Imperfective) and решить (Perfective).