Check out the following playlists. These are a great resource for new officials.
My YouTube Newbie Series (Learn basic high school mechanics)
Gear. Where to get it? You can always get a shirt and whistle at Big 5, but the quality isn’t great. There are many online resources with quality gear. Gerry Davis, Purchase Officials, even Amazon (with free Prime shipping). Locally there is an option as well! Check out Jeff Willis’ The Officials Outlet in Martinez.