I worked in the cattery section, and let me tell you, it's more physical than you think! I don't know how big your shelter is, but in the morning at my one everyone get's into cleaning down about 50 cages which are roughly 6 feet tall and 3 feet wide. Any cats who are allowed to roam about the cattery get let out while we clean, others you have to clean around them. Removing all the bedding/food etc from there. New clean bedding, empty, clean, refill litter trays, new water & food. Work your way from standing to crawling in each cage as you spray it from top to bottom with antibacterial spray, let it dry for a minute, then wipe down the whole cage. Then go to the next one. There were also only about 20 cages in iso, they were a bit easier as they were square cages, but that's where the sick/feral etc kitties were, and harder to work around, or catch if they escaped.
Then you spend the rest of the day playing with them, making sure none of them are being sick, or fighting, that wound sites are cleaned, any medication has been given, meetings/adoptions are sorted and wounds on your own body are sorted to..from slightly irritated kitties! And feeding time is the easiest! Fill up 60 bowls of food and round everyone back up into their cages. Then go home. Did i mention that cats like to christen their clean litter trays all at the same time? dozens of fresh poops in one hit..very smelly. Now who knows, your shelter may be way easier! Or smaller or less occupied.
I suggest good walking shoes, enclosed, ones that you can wash when you get home (either change your shoes before you leave home, or take them off when you get home, do NOT let your kitties touch any soiled clothing either) Change of clothes/wash hands or a shower before you play with any pets in your home at the end of the day.
A big rule i didn't work well with was 'do not get attached to the animals'. They get sick, they get put to sleep for being sick, aggressive, way past repair in an injury, and getting attached while very human, is the most heartbreaking thing ever.
I don't know if this is good advice or not, but that is what i learnt.
On dog training/walking, you need to show them who's boss. If they are jumping up and down on you trying to get your attention you say 'NO, DOWN' in a loud, and firm voice, and when that does not work, you turn around and cross your arms and wait till they stop (this did NO work for me alot of the time, but that's what they tell volunteers to do). If you are in the kennels the whole day you will have to wear gumboots, walk onto wet mats to kill bacteria, spray your hands with an antibacterial gel (same with the cats) you will be scooping/hosing down poo, possibly smelly, possibly from wall to wall (i got a nervous dog who smeared every single inch of his kennel in his feces). Learning the right collars/leads to put on them, how to walk them and distract them from picking fights with other puppies. How to reward them for good behavior, taking them through training yards (ramps, bridges, gates etc)
I'm assuming alot of, or most of what i said applies to other shelters.
Also in my shelter, volunteers had nothing to do with the PTS aspect of animals, they were not allowed to see this. Fine by me, i didn't want anything to do with it.
Hope it helps.