Some verbs are irregular and use what we call the "future stem" instead of the normal infinitive.
Usually, the "a" or "e" vowel which comes before the "r" is dropped. This is the case of "poder" and "haber". Look at the example below:
poder (infinitive) - podr (future stem)
When we add the "future endings," we have the future forms which are translated as "will do something".
Here is a chart for the verb "PODER" in the future:
FUTURE - PODER
yo podré nosotros podremos
I will be able we will be able
tú podrás ellos/ellas podrán
you will be able they will be able
he/she will be able
Yo no podré ir al cine mañana porque yo tengo que estudiar.
I will not be able to go to the movies tomorrow because I have to study.
¿ Podrás ir al cine mañana?
Will you be able to go to the movies tomorrow?
Juan dice que él podrá ir al cine mañana con los muchachos.
John says that he will be able to go to the movies tomorrow with the boys.
Nosotros no podremos ir al cine mañana porque tenemos que estudiar.
We will not be able to go to the movies because we have to study.
Juan dice que los muchachos podrán ir al cine.
John says that the boys will be able to go to the movies.
Yo no sé si yo podré almorzar con ustedes mañana.
I don't know if I will be able to eat lunch ("almorzar") with you all tomorrow.
¿ Podrás almorzar con nosotros mañana?
Will you be able to eat lunch with us tomorrow?
María dice que ella podrá almorzar con nosotros mañana.
Mary says that she will be able to eat lunch with us tomorrow.
Yo creo que nosotros podremos almorzar con los muchachos mañana.
I think that we will be able to eat lunch with the boys tomorrow.
Los muchachos dicen que ellos podrán almorzar con nosotros mañana.
The boys say that they will be able to eat lunch with us tomorrow.
With some verbs, if the vowel in front of the "r" is dropped, we end up with a combination of consonants, either "-lr" or "-nr", we add the letter "d" in front of the "r". This is because of the "trilled" pronunciation of the "r", which makes it difficult to pronounce following "l" or "n".
The "d" is inserted between the "l" and "r" or the "n" and "r" because it makes it easier to pronounce the combination of consonants. Look at the future forms of the verb "tener" ("to have").
FUTURE - TENER
yo tendré nosotros tendremos
I will have we will have
tú tendrás ellos/ellas tendrán
you will have they will have
he/she will have