en_tn_condensed/mrk/04/33.md

he spoke the word to them

The word "them" refers to the crowds.

as much as they were able to understand

"and if they were able to understand some, he kept telling them more"

when he was alone

This means that he was away from the crowds, but his disciples were still with him.

he explained everything

Here "everything" is an exaggeration. He explained all his parables. AT: "he explained all his parables" (See: rc://en/ta/man/translate/figs-hyperbole)