Let's take a step back here and talk about what a restraining order is and is not.
Ordinarily, a person can go anywhere, talk to anyone, and do anything that is otherwise legal for everyone else. I can knock on your door, I can call you on the phone, I can stop you on the street and talk to you. None of these things are crimes, so long as I do not restrict your liberties in any way (you can not answer the door or slam it in my face, you can hang up the phone on me, you can refuse to stop and talk to me).
In some special circumstances, the courts have recognized that for the physical safety of a person, another person's rights have to be restricted in ways that are normally not done. This is a 'restraining order' and it can be either temporary or permanent.
The person applying for a restraining order generally have to show the court that there is a good reason for issuing it. But in domestic cases where violence has been involved, restraining orders are not uncommon.
Now, let us say that you have a restraining order against me, and it states that I am not to contact you in any way, and it further states that I must remain at least a mile away from you at all times.
If I violate that order, and you complain to the police, the police are required to investigate as they would any crime. They take a statement from you, they attempt to located and interview me. If there are witnesses or physical evidence, they collect statements and evidence.
If they decide that there is enough probable cause to believe that yes, I did in fact violate the restraining order, then I may be arrested. As with any crime a person might be arrested for, I will be booked, processed, and I will appear before a judge, who may set bail conditions. If I meet the bail conditions, I will be released pending prosecution.
It may be that the police cannot find probable cause to arrest me. Perhaps you say I showed up at your house, but they interview me and I say I did not. You say I vandalized your car, but I say I did not; and there there is no evidence to prove it was me. In such cases, the police may continue to investigate, but without probable cause, there may be no arrest and no charges. Like running a red light or robbing a bank, if there is no probable cause to believe I did it, then I won't be arrested.
It may also be that I get arrested, processed, make bail, and then return to hassle you even more. Of course I am in violation of the restraining order, which remains in effect. Of course I am subject to being arrested yet again. But this does not mean that the police will follow me around or guard your house. They MIGHT do that - if they believe the threat that I'm about to kill you is great enough. But there are no promises that this will happen, and no guarantee.
It must also be said that often, the victim who obtained the restraining order will choose not to enforce it. Let's say I call you in violation of the restraining order and you don't report it this time. I stop by your house and you let it go without doing anything about it. If I can prove this, your restraining order is worthless - you have to enforce it EVERY SINGLE TIME I violate it, or it will be ruled to have been abandoned by the courts; you don't get to pick and choose when it is in force and when it is not. Many victims do not know this or they forget it, to their sorrow later on.
A restraining order is not a force field around the victim. It's just a 'law' that makes it a crime for the person named on it to perform certain acts or be in certain places. If they break that 'law' then they get prosecuted like they would for any law-breaking. But they don't get locked up to ensure they won't break the restraining order under normal circumstances. That's just not how they work.