Para is the for you already have: when something is for somebody. Por is much more flexible and carries several meanings.
A useful illustration: buy an ashtray and say lo he comprado por ti, because of you. Say para ti and your friend will take it home.
Sometimes English for really means because of, as in for this reason. That is por.
Now the pair makes sense: por qué and porque both contain por meaning because of. Razón is /rathón/ in most of Spain, /rasón/ elsewhere, and it is feminine.
Por esta razón, no quiero ir
The other main use. For two weeks, for three days: never para, always por.
por tres días (for three days)
Me quedo por tres días · Me quedaré por tres días · Me quedaría por tres días
Those three show the ladder nicely: present with future context, then the future tense, which sounds a little more certain, then would.
Día traces back to a very old Indo-European root meaning light. English deity comes from the same root, and so does the ju- of Jupiter, which means something like "father of the gods". Fittingly, Jupiter is the biggest planet.
Note todos goes plural to match: todos los días, against todo el tiempo for all the time.
The -jar of trabajar is pronounced /har/.
The same words work on their own, without a noun following, to mean this one and these.
Este es para ti · Estos son para ti
Remember where the vowels come from: the e of el in este, the os of los in estos.
Stuck on the masculine form of this, the student is not told the answer. The instruction is to go and look at somewhere it has already been used, este auto, and find it from there.
A hook for the -ía ending: pluck it out of me gustaría, which you will use constantly.
Me quedaría por tres días, pero tengo que trabajar.
And building that final sentence, the instruction is explicit: not from memory, but thinking it through again, block by block.