Those/These: 'Estas, estos, esos and esas' Confusion
In English there are two series of demonstratives:
This/these vs That/those
You use the the "this" series for something that is close to the speaker and "that" for something that's farther away..
In Spanish, in contrast, there are three series:
Este (esta, ...) series
Ese (esa, ...) series
Aquel (aquella, ...) series
The "este" series is used for objects that are close to the speaker:
Este es mi pantalón
The "ese" series is used for objects that are close to the listener
Ese es tu sombrero.
The "aquel" series is used for objects that are far away from both the speaker and the listener
Aquellas montañas son muy altas
In general there is a bit of association between yo/nosotros and "este" on the one hand and tú/ustedes and "ese" on the other. This is far from a general rule because it is the distance that is important and there are other associations at play.
However, I think your app wants you to choose the "este" series when used in combination with the first person and "ese" when in combination with the second person.
For example, in the display you show, I think your app wants you to choose "estos" because it is "mis bocadillos".
Again, notice that in practice this is not necessarily true. For example, if I'm sitting on a chair and find out that my coat is hanging from my friend's chair, not mine, I would tell my friend:
Ese es mi abrigo
Because it is placed next to my friend, not to me.
"The "aquel" series is used for objects that are far away from both the speaker and the listener"
This is by far the simpliest and clearest, and therefore the greatest explanation of this.
For years it kept being described as "those (over there)" ie much farther away. I of course could always recognize it and know what it mean, and when I used it myself it was always the right choice, but it was always obvious. I never had as clear and crisp an explanation -- until now.
I'm glad it helped! For completion, let me add that, together with their literal meaning, the different series may also have an emotional connotation.
In particular, the "ese" series may implay a certain contempt:
Eso es asqueroso
The "aquel" series may imply admiration:
Aquella famosa escritora
Besides, in writing the "este" series refers to something that I'm about to talk about, whereas the "ese" series allludes to a topic that I have just mentioned. Not all writers adhere to this particular contrast but I do find it useful:
Hay que tener en cuenta esto:
[Proceeds to mention what must be taken into account
[Writes about a topic]
Y eso es algo que hay que tener en cuenta
A bonus! Thank you!