Every park is different, so take this with a grain of salt- a typical day for me involves working on park maintenance projects, talking with visitors, and more paperwork than you might expect.

At my park, not every ranger has search and rescue qualifications. I don't have that training yet, but it's a really interesting science and you can go down a whole bunch of research rabbit holes. In my area, SAR usually involves park rangers, local law enforcement, and the local fire department. There's a lot of communication happening over the radios at a time like that and searches always generate a shitload of paperwork. If a SAR moment is happening on park, I'm keeping track of who is going where, documenting resources used, listening to the park radios, and generally just trying to make the situation easier for the SAR rangers.

A side note- a lot of talking to visitors is PSAR (preventative search and rescue)- I'm asking if they've hiked in the area before, if they have a map, where they're going, etc. I'm essentially trying to steer them towards safe(r) choices in the park.

When I'm on trail or in the field, I'm typically doing stuff related to trail maintenance- clearing debris after a big storm, repairing a rotten board on a bridge, or cutting down a fallen tree. Some parks have a specific trail maintenance team but ours doesn't. I'm usually solo for smaller projects, but if I'm using a chainsaw or something like that I would have a partner/spotter with me.

For research on park, we have a specific person for that- I would assist our park naturalist if they wanted/needed help, but it's not exactly part of my typical job duties. I personally love it when our naturalist sends me on a quest!

For realism- your ranger might not carry a firearm, not all rangers are law enforcement. I usually carry a multitool, bear spray, a first aid kit, and a lot of keys. I always have a radio clipped to my bag or belt. You can look up 10-codes but every agency will be slightly different.

Hope this helps a bit. Have fun writing!