1. Use the Designations menu (d) to tell your guys where to dig/cut trees etc. Stairs are tricky because you need two sets on different levels that line up. Use Shift + "<" or ">" to scroll up or down through levels.
2. Use the Stockpiles menu (p) to mark areas for storing items. Early ones you might need are an outdoor refuse pile (r) for smelly junk, and a wood pile (w) near your base for all those cut trees.
3. Use the Building menu (b) to place pre-constructed furniture or make workshops (w) etc. If you started the game with the default team, you'll need a Fishery workshop (h) for your fishcleaner to process your fisherman's catch.
4. Learn to use the Look (k) feature to examine things, and the Units (v) feature to look at a a dwarf's skills, wounds, labours, etc.
5. Learn to use the Job menu (j) to see what everyone is doing (or not doing). You can use this menu to jump to dwarves you need to find.
6. Learn to use the Building Preferences feature (q) to change the properties of workshops, stockpiles, doors, tables, chairs, you name it.
From there you can look at what's going on and find out why your dwarves are all dying. Here are the steps I would take for setting up a new base:
- Dig out your base and chop some wood.
- Set up a fishery (if necessary).
- Build a carpenter's workshop and make some beds (which can only be made from wood)
- If you have stone, build a mason's workshop as well.
- Make doors, chairs/thrones, and tables out of wood or stone.
- Make some spare barrels and bins out of wood (you don't have metal yet)
- Set some stockpiles underground for all the crap from your wagon (a custom one that allows everything except corpses and refuse might be useful temporarily)
- Use doors and beds to make bedrooms (or one big dorm if you're lazy).
- Use tables and chairs to make a dining hall. Doors will help to mark where the room ends as well.
Remember: make the furniture at a workshop first, then use the building menu to place it.
Also: Use the Building Preferences menu (q) to tell a bed to be used as a bedroom (individual or dorm), and a table to be used as a dining hall.
- Get a farm set up, and then a still.
Congratulations, now you won't die (until you're attacked). Getting the essentials up and running will allow you to fail at tinker and experiment with the other features.
Since you mentioned farm irrigation, I'll give a little extra info on that:
Dwarf plants require underground farms, and farm plots need to be built on mud. You can leave mud on a floor by flooding it and allowing the water to drain away/evaporate.
Later you might use floodgates and levers to carefully irrigate farms, but there is a rough method you can use to get going.
Dig the room for your farm near a small pool of water (not a river, as the water is infinite!), leaving a single wall between the pool and the farm room.
Once the room is dug out, use the designations menu (d) to channel (h) out the wall from above. The water will flow into the room and thin out, eventually evaporating. Mud will be left behind for your farm plot, but don't try smoothing the floor or the dwarves will clean the mud away.
The only problem now is that you've got a hole that animals and goblins can use to enter your base. Use the building menu (b), the construction sub-menu (capital C), and then "wall" (w) to construct a new wall from some wood or stone.
That should sort you out for now. You'll need to make some fancy plumbing to get water down to deeper levels. And if your only water source is a river, then read up on floogates, levers, and mechanisms to control the flooding. Or, gather some wild plants and use the foreign seeds to make an above-ground farm, which doesn't require irrigation.