I’ve not been arrested but I worked in a bail bonds office, so I know what others go through. At least in Illinois
When you’re arrested, if you’re kids are with you the social welfare of the district (city, county state) is notified and arrangments are made. This was irritating to some people as they were able to get their mum or someone else to take the kids but child welfare gets a report anyway.
If you have a car it’ll be impounded at the arrestee’s expense.
Booking consists of photographs, fingerprints, belongs are stored and documented and your issued “jail clothes”
If it’s a minor charge the police have a choice to set bail or to issue an “I-bond” which is “individual bond,” also called a personal recognizance bond
In Illinois you’re permitted a “reasonable number of phone calls” This is always at least one. And it starts over each time you are moved from station to station or station to lockup. The purpose of this is that the arrested person always can notify someone where they are being held
Bond and bail are different terms. Bail is what you pay to get out of jail till your trial. Bond is the amount you forfeit if you fail to appear. For example if you’re bond is $10,000 your bail is usually 10% or $1,000. If you fail to appear on your date then the court can keep the $10,000 posted.
Bail bonds agencies bond people out and keep part of the bond as a fee. For example where I worked, we kept anywhere from 5% to 20% (depending on the type of crime and the chance fleeing.) So in if the bond was $10,000 the agency would expect to be paid between $500 and $2,000) and that we kept. That was the agency fee whether or not you were found not guilty or guilty.
Public defenders are assigned by the court. You can only get a free public defender if you’re income qualifies for it and it must be a criminal, not civil case.
One thing people fail to realize is, at least in Illinois, over 90% of people using public defenders meet them the day of their case trail or the day before it. You usually don’t spend much time with one.
As for whether or not you have to be told why you are being arrested. It’s kind of a trick question. The courts have ruled you can be held, which is a form of arrest in itself, for a reasonable amount of time. In Illinois courts have ruled this should be as soon as possible but in all cases within 72 hours of being taken into custody.
So you see the phrase “arrested” is somewhat vague.
To a layman being taken into custody is being “arrest” to a legal mind that isn’t being arrest, but being held.
In Illinois the courts have ruled, even when you’re being taken into custody you must be given some basic or general explination of why you’re being held. For instance, “there was a murder in the area and you may be connected to it.”
But in reality you when charges are laid; it could be for the murder, it could be for having your name of a packet of drugs, found on the dead guy, it could be for stealing car that the murder stole off you, you see what I mean. It can be a very “general” reason.
After 72 hours the police have three choices, charge you, let you go or have you go before a judge to have the stay continued. In Illinois the courts have ruled the police can hold you as long as they reasonably feel they need to.
For instance, if after 72 hours the police feel you’d leave and tell someone something that hinders the investigation they go before a judge, state their reasons and you can be held longer. You have a right to challange this detention.
One thing to remember if you say to the police “Am I free to leave.” And they say “yes,” It’s actually up to you to leave. If you choose to stay, the detention is automatically legal.
Of course in real life it doesn’t work this way.
I recall one group of young women our agency bailed out. There were four of them and it involved crack. One of them had a little girl and had to get home, so the cops said, sign a confession and you can go on an “I-bond.” She did it. The other three refused and spent about 24 hours before we bailed them out. Long story short, the cops blew the arrest and the judge threw out the evidence and the three girls got off scott free.
But the one who signed the confession didn’t. And she now has a felony conviction.
See how it works sometimes
The cops can also do things like, “You don’t have to talk to us. You an wait in the holding cell with that enormous man who hates everyone, or you can talk to us and stay on this bench.”
That is one thing that surprised me most about working at the bond agency is how people will sell each other out and make deals with the cops to get any time or chance to leave the police station. You always see on movies, “never snitch.” Maybe that still applies to mafia kingpins but in Chicago, especially “the hood” they sell each other out for virtually any consideration 
went to the same jail. Except once during the night they fed us moldy bologna sandwiches and stale milk. And they keep it freezing ass cold inside so that tempers don’t flare.