Tinkering is used to create various tools from metal (ingots). Use tinker's tools to open the Tinkering Trade Gump. Tinkering, Blacksmithing, Tailoring, and Carpentry can be used in conjunction to make many items.

Gideon's Advice: Tinkering is somewhat expensive to raise. It is also quite useful if you're starting out because you can craft shovels from the ingots you're making to keep your weight low while mining.
From Wodan (optimal):
32.0 - 33.2 SHOWN SKILL = 160 Ingots Tinker Tools
33.2 - 42.7 SHOWN SKILL = 500 Ingots Hammer
42.7 - 66.7 SHOWN SKILL = 2000 Ingots Lockpick
66.7 - 94.0 REAL SKILL = ?? Ingots Lockpicks
94.0 - GM = ?? Ingots Heating Stands

Wodan's Method w/ Documented Ingot Usage
Final skill | Ingots used | Item crafted
33,2 | 160 TinkTools
42,7 | 500 Hammer
66,7 | 2000 Lockpicks
93,4 |5000 Lockpicks
94,3 |500 Lockpicks
97,1 |3000 HeatingStang, Spyglass, Scales
99,3 |3000 HeatingStang, Spyglass, Scales
100 |1500 HeatingStang, Spyglass, Scales
15660 Total Ingots used