看起来and 显得 ， both of them mean " seems like , looks like " , not so much difference .In most cases , they can be switched . eg. 这件衣服看起来有点小 vs 这件衣服显得有点小 . Both of them are ok . But in some particular sentences , it may sounds strange to switch them . eg. 他今天看起来心情很不错（ ok ) 他今天显得心情很不错（ not wrong , but we do not speak this way ） 看起来 is more commonly use than 显得，so next time ,when you are not sure to use which one , you can use 看起来。

1. "请“ is often used when you try to ask someone to do someting . it is sort of formal way .we chinese do not use it to intimate friends . eg : 请帮我递个杯子（ qing bang wo di ge bei zi ) 2. "谢谢” is used when you are going to express your appreciation to someone who helped you with something . It is commonly used . you can say to both a strange or friend , say to everybody even your family . Of course , you can say to the waiter or waitress when you order something to eat . 3. " 不客气“ is used after people saying ” xiexie " to you . It is " you are welcome " in English . It indicates there is no need to say thanks . 4. "对不起“ means apologize . When you hurt , offend someone or something bad happened because of you . You can say " dui bu qi " to that person to show your apology and you want to have his /her forgiveness . These four words are very simple ones to show your politeness , so there is no need to worry that you will over use them . Hope it is helpful to you ! Jack .