Błędnie: Could you explain this text for me? I don't understand most of the words, and there are some difficult structures I've never encountered before.
Poprawnie: Could you translate this text for me? I don't understand most of the words, and there are some difficult structures I've never encountered before.
"Explain" to 'tłumaczyć', 'wyjaśniać'; wyrazu tego nie używamy w odniesieniu do tłumaczenia z języka obcego. 'Tłumaczyć' ('dokonywać przekładu') to "translate'" lub "interpret".