I suspect you are having a pathing problem where your hungry/thirsty dwarves are unable to get to that part of your fort that has food and booze.
Water is only drunk by injured dwarves; they normally prefer to drink booze. Diagnosing and other medical labors are only needed on injured dwarves. Dwarves that are hungry or thirsty are not injured (at least to start with), so medical labors don't apply unless they are very far gone.
If your dwarves are injured or otherwise unable to move, and if your other dwarves have access to a bucket and a water source, can path to the thirsty dwarf, and have the "feed patient/prisoners labor turned on, they should bring water to them. If you have designated a hospital zone, your other dwarves have the recover wounded labor turned on, and they can path to your injured dwarf and to the hospital, they should haul the injured dwarf to the hospital.
Designating a water supply zone at a pond or river or if you have built a well (which is automatically considered a water supply location), your dwarves should use that if they have a bucket and need to water an animal or an injured dwarf.
As to why DF is so complicated, I'll just list some of the may funny sigs I seen on that subject:
Heh. Dwarf Fortress players complaining that something is unintuitive and hard to learn.
DF's got a big learning curve, no, learning cliff, no, a MASSIVE, SHEER EXPANSE OF STONE RISING UP INTO THE HEAVENS, COVERED IN !!Adamantine Barbed Wire!! AND LAVA DROPS, ALL WHILE ARMOK STANDS ATOP AND LAUGHS AT YOUR PITIFUL ATTEMPT TO SURVIIIIIIIVE.
There exist people who learned to play DF without any guide, but these people either got started early when things were simpler and slowly adjusted from there, are some sort of geniuses, or probably belong in a padded cell with no sharp objects allowed.