Use the present indicative to state facts, describe current states, and talk about habitual actions. It is the default tense for most present-tense statements.

Signal words: sé quees verdad queestá claro queveo quecreo que (affirmative)
Pronoun Present Indicative
yo repudio
repudias
él/ella/Ud. repudia
nosotros repudiamos
vosotros repudiáis
ellos/ellas/Uds. repudian

Use the present subjunctive after verbs of wanting, doubting, fearing, recommending, and emotional reactions, especially when the subject of the main clause differs from the subordinate clause.

Signal words: quiero queespero queojaláes importante quedudo queno creo queme alegra quecuando (future)para que
Pronoun Present Subjunctive
yo repudie
repudies
él/ella/Ud. repudie
nosotros repudiemos
vosotros repudiéis
ellos/ellas/Uds. repudien
Key contrast

"Creo que habla bien" (indicative — stating a belief as fact) vs "No creo que hable bien" (subjunctive — expressing doubt). Negation of belief triggers the subjunctive.

Present Indicative vs Present Subjunctive: common questions

What triggers the subjunctive in Spanish?

The subjunctive is triggered by WEIRDO: Wishes, Emotion, Impersonal expressions, Requests/Recommendations, Doubt/Denial, and Ojalá. It nearly always appears in a "que" subordinate clause with a different subject.

Is "creer que" followed by indicative or subjunctive?

Affirmative "creer que" takes the indicative ("Creo que es verdad"). Negative "no creer que" takes the subjunctive ("No creo que sea verdad") because it expresses doubt.

Do present subjunctive forms look like anything else I know?

Yes — -ar verbs in the present subjunctive use -er endings, and -er/-ir verbs use -ar endings. Yo/él/ella forms are identical, which can cause confusion in context.

Practise both tenses with repudiar using spaced repetition.