hey!
For starters, put the shield on a quick bar. you need to "actively" equip it, just like you would an axe/sword or mace, you can also just run around with shield "equipped" and no main hand weapon (for faster running e.g.). So it works like a weapon, not like armor.

A tower shield has more stats than a "regular shield", i.e. bucklers etc, but you cannot perform the "active block" with it. The active block is the timed block, when you do it right, you'll hear a "clash" sound and the enemy gets staggered - thus making regular shields alot better than tower shields imho. Depending on the enemy attack stat, you'll still get damage though, but the better your armor, the less it will be. If you block with a tower shield, it just reduces the damage you will take, but you cannot perform the active block (which i only realized after i got super hyped for an awesome, kinda hard-to-get shield, which turned out to be a tower shield).

I'm not 100% sure if the stagger works if you receive damage though - meaning that unarmored with just a wooden buckler you couldn't stagger a troll with active block, but if you have high enough armor to mitigate the damage when blocking, it should work. Active blocking really makes the game a walk in the park, since it works on every attack and when the enemy is staggered, you even do bonus damage (which makes the sword secondary attack MVP).

If anything changed and tower shields can now active block (or i got it wrong in the first place), pls correct^^