Basically, you have two ways to chop up the entire set of DITA map topics into pages for HTML: use DITA chunking, or use the DITA2Go split mechanism.
DITA chunking uses the same methods as DITA2Go file splitting. However, in effect, chunking inserts Split PI markers for you, and sets file names per any copy-to attributes; see §27.2 Chunking DITA maps. You can use splitting and extracting in addition to chunking.
When you split a DITA file, each piece of the file becomes a file in its own right, typically addressing a single topic; see §27.3 Splitting files.
When you extract part of a DITA file, the parent file is converted minus the extracted portion, and the extracted portion becomes a file in its own right. The extracted part is usually replaced in the parent file by a link to the extract file; see §27.4 Extracting files.