Dreams

I'm really happy because I know I have a good opportunity to travel to another country. I've always had a big dream: travel!
I know is difficult, but if we don't make a purpose or if we don't define a goal, we won't obtain the satisfaction for a of success.

Well written! I just want to make some comments regarding word choice:

"opportunity" your use of this word is completely correct, but in this context it seems that you're implying that you have the current option to go travel, as in, you're making plans at the moment or will be able to participate in something like a study abroad program. If you're not in the process of making plans, I think it is more common to say "I have a good chance of travelling/being able to travel to another country"

"make a purpose" we don't really "make" purposes, but "to have a purpose" or "something has a purpose" so maybe something like "I know it is difficule, but if we don't have a purpose, or if we don't set goals..."

travelling is amazing, and by far the best personal experiences I have ever had. I really hope everything works out for you and that you get to see all the places you have dreamed of! :] suerte!