It's just like unix directory paths. If it starts with "/", it's an absolute path (i.e. relative to the root).

//atom:entry
[download]

is short for

/descendant::atom:entry
[download]

which requests all descendants of "/" (root) which are "atom:entry" elements. You want all descendants of the current node, so you want one of the following:

descendant::atom:entry      # No leading "/" = rel to current node
./descendant::atom:entry    # "." = current node
.//atom:entry               # Shortcut
[download]