It just happened and the news hits you like a runaway truck. You experience a mixture of relief and shock. Relief at having a name for the thing you didn't understand and shock because you still have no idea what to do about it. Better yet, your doctor may not know what you should do either. It's bad enough that parenting doesn't come with automatic instructions, but you have far more to learn than the average parent.
Well you aren't alone and this write up is geared to give you more than one place to start.
I am an adult with autism raising a teenager with autism. I've been on your path and then some. Not only did I have to relearn everything I thought I knew about parenting, I had to relearn myself. This advice will by no means cover every thing you could face. Every child is different and how heavily they are affected by autism is vastly different. That's why it's called "the spectrum". Which leads to my first point:
Get to know your child: Sure, every parent has to do this, but you are watching for intricate details that others will take for granted. You are watching for triggers in sensory that others don't commonly react to. You are watching for extreme behaviors that demonstrate super interest or reaction or almost NO interest or reaction. These will be noteworthy to you so you can help your child interact with a loud and intense world. Look for both the things that aggravate and provide comfort. For example, if hiding under a blanket calms a meltdown, you best have a blanket with you on outings. There are three subjects that I use to teach people about autism in children. They are as follows:
-Sensory: Various sensory (your five senses) "problems" or imbalances are common in autism. Colors and lights may be super bright and overbearing. Sounds may be too loud and invasive. Textures may cause extreme discomfort. Yet, some sensory issues may do the opposite so much that your child seeks them out constantly. These can be very strange behaviors. The list is long and some behaviors can be disturbing. The good news is that your child will develop past hundreds of these behaviors. Behaviors as a toddler are by no means bound to be permanent. And by no means should you think you cannot teach your child alternate behaviors. You absolutely can.
-Routine: The order in which you do daily activities is something your child will likely become very sensitive of. Changes in routines may be met with severe resistance. This includes issues like change of wardrobe from one season to the next. As they grow, clear information on how and why of changes may help. Again, these are teaching points for you as the parent. It's simply something you will have long term work on with your child. The forms of many sensitivities will change with age. Just know, that if you teach them to brush their teeth before getting dressed and one day you switch that around, it may become a very difficult day.
-Social: Social interactions are heavily affected by sensory and some delayed maturity issues (but not just those). Social interactions have a tendency to go one of two directions; too little or way too much. Lack of eye contact or "appropriate" response to your emotions (anger or praise) are just the beginning. Clear and literal information can be of utmost importance. For example, my wife summoned my son to his messy bedroom where he had tossed dirty clothes down in his doorway. She asked him "what is wrong with this picture?". My son became very nervous because, while he saw the mess on his floor, he did not see a "picture" anywhere. If she had asked "what is wrong with these clothes?" he would have understood immediately. You're child will have to be taught very specifically what it means when you are happy with him or not. Just expressing the emotions, will likely not work the same as with a typical child. As an additional caution, never spank an autistic child. It will ignite sensory triggers, cause huge meltdowns, and teach them that it's okay to hit you and others. When I say that you will have to learn a whole different way of parenting it is not a casual reflection.
Be involved with your child: Your child needs you more than ever to help them understand how to live in our crazy world. I'm going to make a suggestion that has helped my own son in so many ways.
Yes, games. I play and collect heroclix with my son. It's a table top game with tiny figurines of comic book super heroes played out on a map. I developed short term variations of the rules for my son to enjoy at a very young age (about 8). It helped him with social interaction, math, and problem solving. He still loves the game to this day. He has fond memories of interactions with those games. How to react to winning or losing and the random chances of the dice are incredible tools that can be integrated into teaching how the world works in real life. It's creative parenting at its best.
Finally, let me tell you that (while you are understandably shaken now) you have become the parent of a very special form of person. He or she is going to show you things about life you never thought possible. Get ready, because it's going to be quite a trip.