When the reporting verb is in the past (dijo, comentó, advirtió), the reported verb moves back one step: presente becomes imperfecto, pretérito and perfecto become pluscuamperfecto, and futuro becomes condicional. A reported question keeps the question word but loses the question marks, and si introduces a yes/no one; a reported order becomes que + subjuntivo.
Examples
- Dijo que estaba cansado y que llamaría más tarde.
- He said he was tired and that he would call later.
- Me preguntó si había leído el informe.
- She asked me whether I had read the report.
- El juez ordenó que se suspendiera la reunión.
- The judge ordered the meeting to be adjourned.
The mistake to avoid
The shift is about the reported time, not a rule to apply blindly: if what was said is still true, the present survives - "Dijo que la Tierra gira alrededor del Sol" is perfectly correct.
Where this fits in
Informar y negociar, Spanish C1: Report what other people said, hold your own in the professional register of meetings and proposals, and read the news: trends, figures and the language of current affairs.