We are going through the simpliest Scout Rush build order (20 pop), and then in depth for civilization variations or faster scout rushes such as the 18 pop Scout Rush. Without further do here is the build order:
Continue making farm, houses and Scouts. Once you get 3 or 4 Scouts you should go attack
Additional advice on how to Scout Rush:
The idea is you make much more damage than what your economy suffers from rushing. If the enemy survives wall up and go to castle, all while still trying to do more damage or wasting your opponent's micro. In castle age your economy should be healthy enough to make 2 town centers, upgrades and additional units. Most of the time it is convenient to keep going cavalry and avoiding your opponents spearmen as you have the right upgrades. However, trasitioning to archers or other unit is also a possibility depending on the civilization you're playing.
Playing against real players is best to learn build orders under preassure. However, you can practice using mods here:
You have to check the in-game time, not the real time. Getting to Feudal at ~9:42 with 21 pop (20 vills and 1 scout) is good. Then attacking with 4 scouts around the 11 min mark is also decent enough.
Keep also in mind there are other Scout rushes depending on maps and civilizations
Scout rush works best in open maps such as arabia or GA and while playing a civilization that at least has bloodlines or better yet, a good civilization for Scout Rush, such as the Chinese, Magyars, Khmer, Mongols or Franks. Also, the scout rush is great for when opponents are not walling properly, and even better if they are going for a Fast Castle.