what do he do on the weekend?改为what does he do on the weekend?he是三人称单数,所以用does
Let's to hiking next sunday改为Let's go hiking next sunday let’s do sth
I can look an elephant改为I can look at an elephant.look at 看
或者改为I can see an elephant,look at表动作,see表状态
The fish are swiming改为The fish is swiming 鱼作名词不可数,用单数