If you hold on to something when the police try and move you, that is resisting arrest, but if you are locked or glued to something and simply go floppy, and leave it to the police to sort out, that is not resisting arrest. It is possible to arrange yourself so that it is very difficult for the police to release you, even if you are not actively resisting, locked high on a weak structure, for example, or lock around your wrist with a metal tube around the arm
The ER advice on being arrested is basically to go floppy, as you cannot be accused of resisting arrest, and are less likely to be hurt, and the police are less likely to be hurt too, rather than if you resist arrest and it becomes a competition about strength. Of course you have the option of simply acquiescing, and walking along with the police quietly - again it is a personal choice, and the aim is for as few of us to be arrested as possible, therefore going floppy ties up more police officers and results in overall fewer arrests. It is up to you though, everything is a personal choice.
Going floppy and being carried to a police van is actually quiet frightening, you are basically trusting the police not to drop you. Generally they don't. but I ask to be carried slung low only a small distance above the ground, so there is less of a fall if they do drop me
You get put in a police van, and typically are there for some hours, and no toilet option 😰which is the worst thing for me at my age! Other arrestees will arrive, and we can chat, but only use code names, the police in the van often chat too, maybe fishing for information, but quite often quite supportive, and friendly, some talk about supporting various environmental organisations themselves - not ones that break the law though!
In the police station, well it depends which one, most are kind and friendly, offer a visit to a bookcase to chose a book to go in with, the cells are generally smooth, without corners, and plain. You then wait hours and hours. You can eat as much as you want, but it isn't very appetising, particularly the vegetarian options! all microwaves meals, just knock on the door and ask.
Eventually you get an interview - again it is up to you whether you cooperate or not, you can give your name, or refuse to, at this stage it is an offense not to, but it is a personal choice. Then you sign your "bail conditions" which may well be that you are not allowed to return to the demonstration - and then you leave and return to the demonstration normally!
I became involved with ER when I saw a demonstration on the news and went up town to support them, and got talking to individual activists, then got pointed to the website and started doing their training