I’ve noticed that english speakers add “up” like a complement of a verb and for me it seems to have the same meaning that without the “up”. So what is that for? I can’t think in any example right now but I think it is true…

Do you mean things like ‘stand up’?
It adds emphasis in some cases (such as ‘stand up’). In others(such as ‘sit up’ or ‘kneel up’) it is necessary for clarity.

HumbertoDeOz can you give us some examples when you find. Thanks!

I think I found one “heat up”… I think that “heat” would be enough, wouldn’t it? It is a verb too. So, why say “Heat it up” when one can say just “Heat it” o.o

As I said above, it adds emphasis.