Vitor, 前面那个饭馆 in English means you can see the restaurant and you are pointing at it, or in general it means "the restaurant a little further down the road"! 不要搞错! "Exactly opposite" is 对面, not 前面! 这里的同学的英语水平很参差。

1) 我们去前面那个饭馆儿吃饭，怎么样？ I think I don't understand the 前面 here... I wonder if the restaurant is in front of the place where the speaker is right now. Am I right? If we're at home for example and we say that phrase, does it mean we would go eat at the restaurant in front of our house? I think it means the restaurant is in front of the speakers location-wise. You see the problem is that in China most people live in apartments and specifically in a community therefore it's kinda weird coz we don't normally live in houses and mostly houses are in the suburbs so I don't think there're normally restaurants in front of houses in China. 2) 这儿怎么了？(there's picture of a messy room beside this phrase) Does 这儿怎么了 mean the same as 这儿发生了什么？ Yes and could also mean 这里（曾经）发生了什么？ 3) 你开出租车多少年了？十几年了。 I don't quite understand the meaning of 十几. Does it mean "around ten" or "a little more than ten"? Or is it something vague? If you've worked as a cabby for 8 years, would you say 十几年了? And if you've worked as a cabby for 12 years? 十几 means ten-ish definitely more than 10 years however less than 20 years. 8 years we would say （差不多）快十年了。 12 would be 十年出头／十几年了. They are both vague numbers and the speaker is also unsure about the accurate number of time or years .

1, your understanding is totally correct, 前面 here means in front of somewhere, this saying is like " let's go to eat at the near restaurant" in English. 2,“这儿怎么了” is " what happened here", but sometimes in different contexts we have different understanding. in later days you will know how to use it in daily life. 3,十几年了，here means over tens years while less than 20 years, and only this meaning. what we say a vague number we say" 几年了“ several years, or when we wanna express about around 10 we say " 十年左右'