Most of these list and describe documents but do not give you full-text access to them. You have to try to get the item on inter-library loan or travel to the library that houses the collection. There are web sites that have only full-text documents. These are frequently not from a single collection but have been gathered from a variety of sources, so that each has to be evaluated separately as to the validity and accuracy of the copy.
Some web sites are simply lists of links to other web pages.
You can use these search tools to locate web sites. However, be careful to fully investigate who created the web sites you find. Many sites are created by individuals who are not historians but have a personal interest in the African American History. Many web sites are also created by companies selling things. Avoid these web sites, and look for web sites created by historians and scholars that are sponsored by educational institutions.