I check the fluids and the reserve was low
Think good thoughts and the problem will turn out to be just low fluid in the clutch master cylinder. Start by filling it to the correct level, and see what happens. If there’s some improvement but it’s still not quite right, get some help and instructions for bleeding the system, and see if it shifts properly. You may find a repair manual at a library, or see if you can get instructions from someone at a parts store. If it does shift ok, then you lucked out: your problem is just the hydraulic system. That will be what you want to happen. Then begin checking the fluid level every day or two until you determine if it’s dropping rapidly or just a tiny amount. If it’s a very slow drop, you may be able to get by with simply topping off the MC when necessary, meanwhile keep careful watch for leaking fluid beneath the MC and from the clutch/transmission area where the slave cylinder is. If it’s leaking fast, you probably need to replace the master and / or slave, or ideally both, as @ok4450 wrote.
If it won’t shift properly after you fill the system and bleed it properly, then you bite the bullet and pay someone to replace the clutch. Get it towed if you can’t shift without grinding gears.
I had an old Nissan truck which had a very slow leak somewhere in the hydraulic system. Mind you, that 4cylinder truck was used to pull heavy loads uphill, including a trailer with chunks of concrete at least twice. Every now and then, the pedal surprised me by being soft, and shifting was a little dicey. All I did was fill the MC and pump the pedal and it would be fine for so long that I’d totally forget about it. This would happen every couple of years because I would never remember to check the fluid. I probably drove 75,000 miles with it like that, and maybe had to refill the MC three times, which might have cost me at most a grand total of 15 minutes. That’s all I ever did. I had to retire the loyal truck for other reasons. I hope you are equally fortunate.