Union apprenticeship sign-ups near Boise after 6 years as an HR coordinator

The training centre near Boise opened applications for apprenticeships in electrical and welding trades. This is my first time dealing with any of this. The application needs a diploma or equivalent, a driver's licence and a short aptitude test. What do you wish you had known?

The aptitude test was mostly maths and reading a diagram. Free practice tests online were enough for me.