So on low res.
You should build a hall as close to the gold mine as possible, then a farm (but don’t put anything between the hall and mine). Then send the peon to get gold and make another peon. Send the next one to get gold and make another when you can. Keep making peons till you have 5, having the last three get wood. When you have 250 wood, take a peon who just returned with wood and make a farm.
Now there are many different strategies, so you should play around to figure out what works well and what doesn’t work. Playing around with where you send the next peons (gold or wood) will halp you when you have different starting resources (map default, medium, or high), and you will soon realize what seems to work best.
The three farm rax means make three farms before you build a barracks. The four farm rax means make four farms first. Of course the 3 farm rax will get grunts faster but at the price of peons and future speed…one important figure to keep in mind is that it takes 3x as long to chop wood as gold, so if you have one peon on wood and one on gold you can expect to get 100 wood by the time you get 300 gold.
Also if you can wall in (use trees and buildings – not walls – to prevent the enemy from getting to your peons), you might consider walling in and making a lumber mill instead of a barracks. If your opponent attacks, repair the buildings to keep him out and make a tower to protect them. Don’t forget to leave yourself enough room inside the wall in to make the buildings you will need (barracks, smith, mound). You can also chop to make room, but if you have to wait to build something because you don’t have room, you are either playing mini chop chop or you are going to be in trouble.