Wizards have a number of skills that grant shields. They all grant shields as a % of your max life. And function basically as an extension of your health pool (so benefit from all your sources of damage reduction). Increasing your max life means each skill with grant you are larger shield, since it’s percentage-based.
The skills are:
Magic Weapon: Deflection
Spectral Blade: Barrier Blades
Galvanizing Ward
Dominance
Diamond Skin
With Magic Weapon: Deflection and Spectral Blade: Barrier Blades, they grant shields when you attack that last for 3 seconds. If you attack faster, you can get more shield stacks active at the same time before they start to expire. (Side-note: this is part of what makes Deflection so good for Vyr’s Archon. You attack really fast and get lots of shield stacks). The other skills are pretty self-explanatory. Blood Bracers increase the shield value from all those wizard skills.
There are a few other places you can get shields from, however Blood Bracers won’t buff the shields from these other sources. Blood Bracers only work on shields from wizard skills. A couple of examples of non-wizard skill shields are the level 25 effect from a Molten Wildebeest’s Gizzard gem and the active effect from the monk Mantra of Healing. These can increase your shield further, but won’t benefit from the Blood Bracers bonus.