Speaking from my experiences (US)
I've been hospitalized four times for attempts. Once voluntary, the other three were involuntary. Been to three different psych units in hospitals.
Like with anything, things will be slightly different based on location but they're all the same for the most part.
One thing I will say is to avoid psych units in cities/metro areas, request one in more rural or remote area. I've never been but I've heard from other patients that they suck for quite a few reasons.
You'll usually share a room with one other patient of the same gender, or you might get lucky and have a private room. Bed quality dependent on facility.
The other patients will totally vary based on who happens to be there at the same time as you; completely random chance. Some are they voluntarily, others involuntarily brought in by police or EMS. You'll have other suicidal people, ones in for drug problems waiting to go to rehab, someone who just had a panic attack or breakdown, schizophrenics and the list goes on. You might meet decent people, and others you'll absolutely want to avoid.
You'll have the standard three meals a day. Food quality entirely dependent on the facility. Some places were terrible, others actually pretty good. They'll usually have snack times in between meals to keep you tide over.
They'll generally always have a TV room in a common area. Others will have games, activities and books (I learned how to play chess when I was in). But there's only so much to do and you will get very bored, very quickly. They typically do several group therapies through out the day covering various mental health topics.
Staff are usually referred to as 'techs' or 'aides', and are always present to supervise and monitor patients. They do rounds every fifteen minutes to make sure you're safe and to document what you're doing.
You'll be given gowns/scrubs to wear initially. But you can wear your own clothes as long as they aren't "inappropriate" and/or don't have strings. No cells phones. If you're a nicotine user, they'll give you lozenges or gum.
You'll meet with a psychiatrist once a day. In my experiences, most times, they are very snobby and arrogant. They'll add, adjust and remove medications as they decide. You may also meet with a social worker every few days depending on if your situation calls for it.
As I was there involuntarily three out of four times, I do not have good things to say about psych units or the people who run them. I've found the doctors, social workers and administrators to be very cold and hearltess while pretending they care because it's their job. Some of the nurses and technicians can be cool. But I did attempt to be as neutral and objective as I could. Hope this gave you an idea of what they're like.