Really? This page?...
http://www.dwarffortresswiki.net/index.php/Workshops_FAQ#How_do_I_make_glass.3Fglass - you have haulers gather sand in bags from a designated zone (< i >, just like setting up a drinking area or refuse heap). You make glass from the sand. (Any questions so far?)
(If you want
clear glass, then you also make ash at a wood burner, turn that into potash at an ashery, then pearlash from that at a kiln, and
then make clear glass with that and the sand.)
Sand (gathered from designated collection point) -> glass
Wood -> ash (woodburner) -> potash (ashery) -> pearlash (kiln) -> clear glass
Green glass is only worth 2 - same as flux, less than obsidian. Clear glass is worth 5 - one more ingredient for 2.5x the value? It's worth it if you have the trees to make the pearlash.
If you're going to just use it to train gemcutters/setters or glass makers, then yes, use green. But once you've got the industry in full gear, go for quality.
Soap - you make ash (by burning wood), then you make lye at an ashery from that. You make tallow from fat (which you get from butchering animals) at a kitchen. Then you make soap from tallow and lye.
Wood -> ash (wood burner) -> lye (ashery)
Dead animal -> fat (butcher) -> tallow (kitchen)
lye + tallow = soap
It's like steel - you won't see the items in the menu until you have all the necessary ingredients for the last step.