What is the difference between verbs COB and HECOB?and how can i use these verbs?and when i must us?
i dont know the difference between them

Question

Answer

COB and HECOB

COB — совершенный вид —СВ 
HECOB — несовершенный вид — НСВ

Russian verbs have 2 aspects: 
 imperfective (несовершенный вид — НСВ) and perfective (совершенный вид —СВ )

For example: 
делать (imperfective) — сделать (perfective)  — to do
читать — прочитать — to read

Both verbs (НСВ and СВ) describe the same action, BUT:
imperfective (несовершенный вид — НСВ) verbs describe only the action;
perfective (совершенный вид —СВ ) verbs describe the completion, ending or result of the action.

Я читал книгу — I read the book
Я прочитал книгу — I finished reading the book

http://www.italki.com/entry/386787

Answer

Your question is very difficult to explain. I am Russian and I never make mistakes in using of aspects but it is impossible for me to explain this theme. You need a good Russian grammar book or sites for learners of Russian as a foreign language.