There are many ways it can happen for a player. Some go to a college camp and that does it. Some are actually seen playing in a hs game. Some are seen at a showcase or a showcase tourney. Some are seen at a legion game etc etc. But there is no doubt that playing on a summer / fall team that gets you out in front of college coaches from all levels will give you the most opportunities if you can play.
My son was recruited by his college program based on camps and later they attended a couple of hs games. He had other opportunities based on performances at WWBA events and with his showcase team in tourneys. I know kids that went to a college camp and were offered based on their performance at the schools camp. To me its all about creating as many options for the player as possible. I understand that some can not afford to everything others can do. But there are plenty of opportunities out there for everyone.