can we go to macau from guangzhou for a day trip? how do we go from there?

Yes, you can have a day trip in Macau.
There are direct bus that can take you to Macau. You can take it at Dongfang Hotel and arrive at Macau Tower. It's very convenient. It will take 3.5 hours on the way.
Or you can take light railway at GZ South Railway Station, and go to Zhuhai Railway Station. After arriving, walk to the Gongbei Port and pass the custom. Then you can start your trip in Macau.
It will take an hour on the way.