POLICE: Stereotypes mean that some policemen are more likely to shoot and kill black people than white people, blacks are frisked more, blacks are stopped on the roads more, etc.
DRUGS: Blacks are more likely to be arrested for drugs, war on drugs has been a failure that targeted black people.
PRISON: You get the idea here. The first two should make you understand why more black people are in prison.
EDUCATION/HOUSING: Most black people live in 'the hood' because of redlining. Education disparities make education worse there. Neverending cycle.
WEALTH: This all kind of leads to black people being much poorer on average than white people.