Exactly! Depending on your job the importance of the grammar will be, but in general is a good idea to improve the grammar everytime that is possible, good luck!

El programa se llama "yo sobreviví"

Estoy viendo un programa donde las personas se mueren y visitan <strike>al</strike> el cielo o el infierno y entonces se vuelven. Esta noche un hombre se fue al infierno y dijo que fue muy malvado y tuvo fuego. Yo no sé si creo que estas historias son verdaderas pero son muy interestantes para ver.

Your spanish is very good! and yes that stories are hard to believe hehe

When the context is to send something, a letter for example, both are correct, but "mandar" can has other meaning depending in what context are you using it, "mandar" means command too. Cheers.

First notebook entry: Introducing myself

My major is international trade and econonomics, in the future I will work with foreigners, so English is extremely important to me, however, after graduating from high school, my English has gone backwards. And now there is one year left before I graduating from university. I am eager to improve my English. I wonder if anyone would help me, I will appreciate it. (Punctuation signs)
Done! I hope we can practice english some day!

Of course satisfaction! If you feel really good doing your job I think you have more chances of be well-paid for it. Cheers!