Let me guess, you have just started working on site, and the guy looking after you likes his jokes?
Safety boots are chemical resistant, have electrically insulated soles, and steel toecaps.
So if you step on live wires, walk through a chemical spill or something drops on your foot; you'll be alright.
They work so well that without them sites are more dangerous because people forget that someone may not have boots.
I often use mind to rest a ton or so on, that way I can get purchase underneath when I need to lift it. hate to think what would happen if I ever forget to wear them.
One tip, I usually find that a size bigger is best - that steel doesn't have a lot of give.
As an Engineer I get my pick of styles from the stores - saves me money in hiking boots. Though I tend to skip and jump along when I return to trainers.