Nobles (monarch/mayor/baron[in its various forms]) issue mandates to produce what's usually junk. These mandates are based on their preferences, so if you manage to find a dwarf that has no preferences for items you'll get a lot fewer mandates. In the case of picks you can just melt those down to reuse the metal for the next mandate (which is probably going to be more picks...). The really annoying mandates are the ones where they order junk like scepters, which you can't produce directly, but have to order "crafts" and just hope you get some scepters, rather than just place the order and forget about it (and order more junk as the mandate wasn't fulfilled).
Open space magma 7/7 means the tile you looked at is completely filled by magma (7 out of 7 depth in the tile, the same as for water), and the open part means there is no floor on the tile.
Magma is used to power magma versions of powered workshops. However, I think those aren't visible in the workshop/furnace menus until you've discovered a magma source. Magma is used by the workshops by building the workshop with at least one tile above an open magma tile (i.e. a hole in the floor with magma directly below). You want to plan the building/digging such that you have a single open magma tile and the workshop is placed with its impassable tile (usually darker in most/all(?) tile sets) directly over the magma tile. That will ensure dorfs can't fall down into the magma, which is usually considered a good thing. Magma workshops get power when the magma depth in the tile below them is 4/7 or more.
I'd recommend not to build workshops directly on top of the magma sea, but rather drain some magma off into a tunnel that is then sealed by a magma safe raising drawbridge (ALL components of the bridge have to be magma safe: stone(s) as well as the mechanism or the bridge will get destroyed over some limited time if not raised).
Locate the magma sea. Find a place where the magma meets rock (i.e. a "shore"). Go up one level and dig a a single tile channel down into the rock and then a tunnel up to, but not through, the wall to the magma sea (You can do this on any magma level, as magma isn't pressurized unless pumped, in contrast to water). Once you've dug your tunnel you build a magma safe drawbridge by the wall to the sea (I actually use 3, one for workshops, one for a magma filling station [for hauling magma via mine carts], and the outermost one for a magma pump stack. Note that I only provide for these. Whether I actually build them is a later question). You should also channel holes in the floor above the tunnel (you'll need to dig this out for your workshop area) so you know where your workshops should be. I then build them as soon as I've made the holes.
Note that access to the magma sea can let hostile critters in (hence the drawbridge(s)), so you don't want any open holes in the workshop. Note that magma is capable of powering a workshop indefinitely, as it doesn't cool off.
I actually embark on metal free embarks and rely on invaders to provide me with metal (except a small supply of junk metal to be used for moods before invaders arrive), but that requires a reasonably careful embark selection to make it probable they'll arrive (and a desire for sieges, of course. Some DF players want to build their mega projects without being disturbed). I also make sure to have sand available on my embark, as that can be used for cage traps and menacing spikes, of which I use copious amounts.