Even if you went with the absolute best temperament on the parents of your puppy. And you got the calmest puppy in the litter. But you simply set him outside all the time or in a crate (all the time, specifically while you're at work or at night is fine) you'd end up with a nightmare. Socializing is a big commitment but an absolute must when bringing a Rottweiler into your family.
There is absolutely a risk of contracting disease or parasites. So, I'll cover what not to do first. Do not go to dog parks before your puppy is at least 1 year old. If you plan on having him or her neutered or spayed it's a good idea to do that after 1 year but before venturing to the parks. Dog parks are a great idea in theory but not always so in real life. People bring sick dogs to dog parks. Either because they don't know the dog is sick or they simply don't consider the risk. People bring unsocialized or aggressive dogs to dog parks. Either because they think this is how to socialize them or because they simply don't consider the risk. Don't be that guy.
Once your puppy has had all of his puppy shots and his 1 year and 16 week booster (done 1 year after the last shot at 16 weeks of age) you have more protection from disease. To avoid parasites choose parks that are large so mess is spread out and parks that are cleaned often. Keep your dog from eating anything at the dog park! A seriously good Leave It cue will be your best friend when trying to avoid snacking in a field full of poo.
If you can't go to a dog park then how do you socialize your puppy? Well, let's start with the home field advantage. Bring the socializing to your puppy. Have friends, family members, neighbors, etc come over to meet your puppy. Likewise take your puppy to their homes to meet them. New people, new places, new smells, and practising your cues under high stimulation will make a huge difference in how easy your dog is to handle as an adult.
Invite over or go visit dogs you know to be safe. Ask friends and family members about their dogs, watch their behavior, make sure they are not sick and are vaccinated. Then, let your puppy interact with them. Dogs learn how to behave with other dogs by hanging out with other dogs.
Another great place to meet other dogs who are healthy and social - or at least on their way to becoming social - is a dog training center. Take obedience classes or conformation classes to expose your puppy to lots of other people and dogs. Find a center that requires health clearances before admitting puppies to their classes. For extra safety, start these classes after your puppy has had his or her last vaccination at 16 weeks. Also don't be afraid to visit the veterinarian and pet stores, but hold you puppy up off the ground until he or she has had all of their vaccinations.
Socializing isn't just about people and dogs. It's about how your dog handles new situations and stimulation. Practice your basic commands (Sit, Down, Stay, Here, Leave It, etc) first at home until she's got them down and then in public places with lots of noise and stimulation. Try dog friendly restaurants, regular visitor parks, marinas or rivers with walking trails, beaches or camp grounds, etc.
If your dog is very suspicious or nervous you know you need to do more. Don't force it on him. Gently ease him into situations that are new and possibly intimidating. Reassure him but do not guard him. Do not pick him up. Do not block him from the outside world or reassure his suspicions or nervousness. Let him think a moment. Keep calm and help him calm down and then just move on like nothing happened.
Lastly, don't forget about handling. Part of your socializing should include handling your dog. You'll pet her all the time, sure! And you'll probably pick her up and snuggle until she's too big to do so. But go a step further. Handle her paws and all of her toes so that nail trimming is easy when it's time. Nothing like a 120# rottie freaking out when you try to touch her nails! lay her on her back and firmly hold her if he struggles. Don't hurt her! But be dominant. It takes a lot of submission and trust to accept being the one on your back because all of your vital parts are exposed. Use a cue work to mark the behavior like "Over." Open her mouth and touch her gums and teeth. Is might seem dumb but if you need to clean them or she has to have work done on them you're going to want to be able to get in there without getting bit. And it's a lot easier to teach a puppy than an adult! Use a cue word to mark this behavior as well such as, "Open."
With some careful screening you should be able to find a breeder who begins a lot of socializing for you. Our puppies will easily meet 100 unique visitors before they are 8 weeks old which can include puppy families, friends, our own family, neighbors, even the UPS guy or the realtor! I'll spend a lot of time handling their paws and their teeth as well as laying them on their backs. I'll discourage them from biting and allow them to spend time with all of my Rottweilers of all ages as well as some family dogs who I know to be safe and healthy. It's your responsibility after they go home to continue socializing.