Install a The Lost World of Warriors server through the Control Panel (Servers → Select your server → Game servers → Add Game Server → The Lost World of Warriors)
Honestly wasn't expecting much after hearing it lagged a lot from friends trying this site, but after using it for about a month now its pretty smooth. Modpacks that aren't as big as ATM10 barely lags or causes friction. Pretty easy to navigate through the whole site and got enough modpacks to not get bored.