Préterito Perfcto versus Presente Perfecto

Tenía una larga conversación con una amiga. Ella no es una hablente nativa de español - es de estados unidos - pero dice que había estudiado él durante mucho tiempo. La conversación era de las deferencias entre préterito perfecto y presente perfecto...y de debería o no debería usar préterito perfcto con ¨Hoy¨. Voy a presentar que le dice y me gustaría saber que es el opinión de los hablantes nativos de español.

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The pretérito perfecto and the presente perfecto are not the same thing. The second website you have there is incorrect. Here are all the perfect tenses with examples:

Present perfect indicative: He salido. I have left. Past perfect indicative (pluperfect): Había salido. I had left. Preterite perfect indicative: Hube salido. I had left. Future perfect indicative: Habré salido. I will have left. Conditional perfect indicative: Habría salido. I would have left. Present perfect subjunctive: (que) haya salido. (that) I have left. Past perfect subjunctive: (que) hubiera salido. (that) I had left
Notice that in your podcast it asks what you´ve done this month. For el presente perfecto, you use this to indicate something that happened at some unspecific time in the past (something you have done before now, or at this moment). It makes sense then to use it to tell someone what you did that month, since you did them before you were talking to that person. It isn´t used for something where you specify the time, like when you begin the sentence by saying "hoy."

For example if someone asks you if you´ve gone to a specific grocery store before, you would say you have or have not gone. If they ask if you´ve gone to the grocery store yet today, you would answer you did or did not go. This tense functions the same way as how you would respond in English. Does that make sense?

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¡Muchas Gracias!