Someone said to me we cannot blame "Satan" for everything. We have to blame our "flesh". Can you tell me what does our flesh represents or mean.
We can certainly blame Satan for many temptations that we face. As was indicated to you, we should not blame Satan for our giving in to those temptations. We decide for ourselves whether or not we fall because of the temptation. “But every man is tempted, when he is drawn away of his own lust, and enticed. Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.” (James 1:14-15) If we resist Satan we won’t succumb to temptation. “Submit yourselves therefore to God. Resist the devil, and he will flee from you.” (James 4:7) The devil can not make you do anything.
That being said, let us look at the question you actually asked. What is meant by “the flesh” as concerns sin.
The apostle Paul is the one writer who most uses the word to mean, in the words of the Greek lexicon used by www.blueletterbible.org, “mere human nature, the earthly nature of man apart from divine influence, and therefore prone to sin and opposed to God.” Paul especially argues in Romans, chapters 6-8, that we have two competing natures, the flesh and the spirit. When we follow our fleshly nature we are not following God, but our lower desires. In chapter seven he says that our spirit actually desires that we do good, but sometimes we let our flesh take over and then we do what we don’t spiritual want to do. That is sin.