# what Joab ... did to me, and what he did

"what Joab ... did to me—that is, what he did"

# shed the blood of war in peace

"killed those men during a time of peace as if he were killing them in war" or "took revenge on those men during a time of peace because they had killed people in war" 

# put the blood of war on the belt around his waist and on the sandals on his feet

Joab was close enough to these men when he killed them that their blood spattered on his belt and on his sandals or the word "blood" refers to guilty of murder, and the belt and the shoes refer to Joab's authority as commander. David is saying that because Joab is guilty of murder, he should not be commander of the army. It is best to translate this literally.