It's a great way to travel: fast, easy and very comfortable. While there are security checks before boarding, they are quick and the queues are minimal for a baggage scan and a walk through a security arch. The waiting areas at most stations have all the needed facilities: bars, restaurants, shops, etc.
There is ample online information on the AVE network, so this can be short, facilitating links to the resources you'll need to find out more detail and even book your next trip. I'm a big fan, and like to use these trains whenever possible. From Madrid I can travel to Barcelona or Seville in just 2 1/2 hours.
The high speed rail network carries the high speed AVE, Avant, Alvia, Avlo trains and also the mid-speed Altaria version. Some routes are non-stop, others have intermediate stops along the way. The stops are short and cause only a minimal delay. For example, Madrid to Seville with just one stop in Córdoba takes 2 hours 32 minutes, with four intermediate stops 2 hours 45 minutes, only 13 minutes longer. The trains run reliably and on schedule. Free Wi-Fi is an added bonus onboard the AVE trains, and is available in most train stations.