"I don’t like to speak with a quiet voice it’s like I was hiding out in my own room." 

Correction: "I don't like to speak quietly."   

    You speak with your voice, so it is unnecessary to state both in conversation.

Correction?: "It feels like I was hiding in my own room."

    You said "It's", which is a conjunction of "it is". I'm not sure what you're referring to when you saying, so I'm not sure my correction is helpful. (: Sorry!

"My friend and I are planning to visit another friend, he lives in Santa Marta, which is a very dangerous place."

    Technically incorrect. This is a run-on sentence. It should be: "My friend and I are planning to visit another friend. He lives in Santa Marta, which is a very dangerous place." When you have a break in a sentence, like this, the wording in between commas has to relate to each part of the sentence. 

    Conversational Correction: "My friend and I are planning to visit another friend in Santa Marta, a very dangerous place."

"Like three days ago my mom asked me to buy a new hose for the bathroom sink, because its hose is already broken, that’s why it isn’t working."

    Technically incorrect. Another run-on sentence. Be careful not to add too many commas to a sentence.

    You also should say "about" or "approximately" in place of "like". Saying "like" means there is a synonym, and in this case there is not. I     know it is confusing because "like" is also slang. However, it is still grammatically incorrect. 

    Here are (some) ways you could state this:

    "About three days ago, my mom asked me to buy a new hose for the bathroom sink. It was not working because the hose is broken."

    "My mom asked me to buy a new hose for the broken bathroom sink about three days ago."

    "The bathroom sink broke approximately three days ago, so my mom asked me to buy a new hose."

"It gets really hard not to brag when I get a good grade."

    Correct. I don't see anything wrong with this sentence. Good job!

"Yesterday I was watching the most depraved metal album covers on google images."

    Technically incorrect. I might be misunderstanding what you're saying, but you watch videos. Watching usually implies movement. For example, if you were to go to the movie theater and buy a ticket for Finding Dory, you would say: "We are going to watch Finding Dory." If you were searching for an image on Google, you would say: "I am looking for an image on google." Does that make sense?

    In other words, your sentence should read "Yesterday I was looking at the most depraved metal album covers on google images."

I hope I was helpful. If you need any clarification, let me know! You did great.