Here's another example from Level 5:

Let’s go surfing on Saturday because (it)’s going to be hot and there will surely be a lot of waves.

Vamos a hacer surf el sábado porque va a hacer calor y por seguro hay muchas olas.

Why is the present tense "hay" used instead of a future tense? BTW, Google Translate translates that sentence as:

Vamos a surfear el sábado porque hará calor y seguro habrá muchas olas.

I was having the same problem at those leves. Every time I came across the phrase "allá", "aquí", "de allá" and "de aquí", I made a note of the English and Spanish phrases. It seemed to me that the "de" is needed when the "here" or "there" refers to something more general rather than a specific place. See some usage examples below that I collected. I also have a note (not sure which lesson this is from) that the preposition "de" is needed when you could say "that is here" or "that is there".

Examples from the lessons:
That necklace there is very nice. How much does (it) cost?
Ese collar de allá es muy bonito. ¿Cuánto cuesta?

(I) bought a very nice necklace for my friend(f) at this store here
Compré un collar muy bonito para mi amiga en esta tienda de aquí

No problem, I can wait for you there
No problema, puedo esperarte allá

este de aquí or ese de allá
this one here or that one there?

tuvieron cuatro reuniones allá
they had four meetings there

pero después abrieron una oficina nueva en bogota y tuvo que ir allá
but afterwards they opened an office in bogota and she had to go there

Estan allá, a la derecha
(Referring to some necklaces in a store) They are there, to the right

Ellos van a estar allá unos días
They are going to be there a few days

en esta tienda de aquí hay algunos pareos preciosos.
In this store here there are some gorgeous beach wraps