What were some of the challenges that ex-slaves faced in the US after they were freed?

The American
nation did not make provision to integrate the freed blacks into society.  They were treated in
the north and west, and by the nonslaveholders of the South, as a pariah.

Many or most of the northern and western states had laws forbidding free blacks from
entering.  These states also had laws limiting the political and economic rights and
opportunities of the free blacks that already lived there.  Pretty soon, the South started
copying those laws.  Upon being freed, the only friend the blacks had was their former owners. 
After the Republican party used the blacks to put itself in power in the southern states, even
their former owners no longer thought well of them.

Under slavery, blacks had
food clothing and shelter from cradle to grave, in sickness and in health.  Under freedom, they
had these needs only so long as they could work, and very many of them had not had any training
or education under slavery that would help them cope with freedom; furthermore, they were
subject to laws that limited their movement and what jobs they could hold and so on.  It was one
generation before the southern whites recovered the average economic well-being that they had
know before the War Between the States.  It was three generations before the southern blacks
recovered the average economic well-being that they had known before the war.

The nation did not help them to homestead lands in the west, because western whites did
not want them there.  The nation did not break up plantations in the South to provide them
land.  (That would have been unjust to the owners, but the reason was that the nation wanted
cotton produced on those plantations, and small farms would not have been very good for
this.)

Two references:

Donald, Henderson H. 1952.
The Negro Freedman: Life Conditions of the American Negro in the Early Years after
Emancipation. New York: Henry Schuman. I found this book in a university library
near-by to my home. Your school librarian might be able to borrow it for you via Interlibrary
Loan, or you may visit a nearby university library yourself. If it is a state university, it
will probably let you check the book out yourself.

Livingston, Donald W.
2010. "Why the War Was Not about Slavery," Confederate Veteran,
68, 5 (September/October), 16-22 & 54-60. If you can't find a copy of this article, send me
a message, and I can send it to you.