He/She/It = S after all verbs?

Hi, everyone.

I am Lucas, I am from Brazil and I speak Portuguese as my first language.

I've been learning english for 8 months, therefore, I have many doubts still. I keep comparing English with Portuguese and I've concluded that Portuguese is too complex to compare with english, and it is pretty bad to me, because I get confused all the time.

Here's my question:

For He/She/It in English we add a "s" after the verbs. In Portuguese we have a similar rule, but "the S" comes in different usages, e.g:
The person will get home at some time and I am telling someone what I'm going to do when that person arrives(or arrive)

When "Jack" comes home I am going to have a conversation with him.

That "comes" is supposed to mean he'll come at some time, and not something he does, like: He comes home everyday at 7pm.

So, I would like to know if I'm wrong (quite sure I am) and if someone could explain to me.

Really sorry about that bad explanation and about my english, but I don't really know how to express my doubt and also I'm a "newbie" at English.

Thank you, Lucas.