In theory this is easy:
This/these is the English proximal deictic demonstrative determiner and pronoun. It represents the nearer (less distant) of two possible distances with respect to the speaker.
That/those is the English distal deictic demonstrative determiner and pronoun. It represents the more distant of two possible distances with respect to the speaker.
In practice, especially in your personal case, it may not be easy at all.
Iberian languages like Portuguese, Spanish, and Catalan provide three grades of locative deictics — not just two like you find in most dialects of present-day English. Where English now has only proximal and distal grades, Iberian languages also have a medial grade. See here for Portuguese.
||first, like where you would use my
||something here close to me
||isto, este/estes, esta/estas
||esto, este/estos, esta/estas
||second, like where you would use your
||something there close to thee/you
||isso, esse/esses, essa/essas
||eso, ese/esos, esa/esas
||third, like where you would use his/their
||something over there (yonder) close to him/them/neither you nor me
||that/those (yon, yonder)
||aquilo, aquele/aqueles, aquela/aquelas
||aquello, aquel/aquellos, aquella/aquellas
So the first problem you encounter when translating is that you need to map three grades in an Iberian language to only two grades in standard English.
But another issue is that some speech communities assign these grades differently, particularly in Brazil where you may be coming from. If so, then your instincts and regular translation directions may not serve you well here.
See also: 1, 2. In particular, the latter mentions that:
No português coloquial brasileiro, "isso" e "isto" são usados como sinônimos, sem que se faça diferença entre eles, mas com grande preferência por "isso". A situação é análoga para essa/esta ou este/esse.
Rather loosely translated, that runs more or less like:
“In colloquial Brazilian Portuguese, "that" and "this" are used as synonyms, without any difference made between them but with strong preference for "that". The situation is analogous for [the gendered inflections of both those two words].”
Meaning that colloquial Brazilian makes isso (that) and isto (this) synonyms! Eeek! This is going to be very confusing for any instincts you could possibly have. Do please read that answer for more about all this.