i wrote some sentences,please point out my mistakes

Food has been eaten up,go out and buy something.

All the food is gone/There's no more food, go buy something.
since you said that ,put you words into practice

well, since you brought it up, why don't you go shopping?
it will take us at least two hours to take a bus to get there

It'll take us at least two hours [if we take the bus/to get there by bus]

we failed,but at least we tried

We failed, but at least we tried
speak louder ,let everybody hear you

Speak louder so everyone can hear you (what you wrote is also correct)
how much time did you spend on that article

(what you wrote is correct)
you seem to be sad,tell us what has happened so that we could help you

you [seem to be/look] sad, tell us what (has) happened so that we can help (you)
my brother is coming to beijing,he will get most out of time that he`ll stay here

My brother is coming to Beijing, (i'm not sure what you are trying to say)
you are the people i`m looking for

(what you said can be correct, but it depends) You are the people for whom I'm looking