How to check does polygon with given sides' length exist? I have polygon with $n$ angles. Then I have got $n$ values, which mean this polygon's sides'  length. I have to check does this polygon exist (means - could be drawn with given sides'  length). Is there any overall formula to check that? (like e.g. $a+b\ge c$, $a+c\ge b$, $c+b\ge a$ for triangle)

No, there's no overall formula. There are some weak conditions (the sum of any $n-1$ sides' lengths must be greater than the length of the remaining side, for instance), but this is merely necessary for the existence of any polygon with those side-lengths, not one that has your desired angles. Is it sufficient? I'm not certain offhand. 
Re-reading, perhaps when you said that you "have "n" angles" you meant "I'm looking for an $n$-angle polygon". 
In that case, the inequalities I cited above are necessary, but are they sufficient? I suspect that they are, although they'd only guarantee a polygon with those side-lengths...not a non-self-intersecting polygon. For that latter condition, you'd have to do some additional work. 
