Can shields stack? As in, if I play a Stalwart Poro and Taric at base, is the Poro at plus 1 or 2 shield?

Yes, Shield values stack additively.

According to Rule 814.2: "If a Unit has Shield, or has been granted Shield, and is granted Shield by an additional source, the Shield Value of all granted Shield keywords is summed."

In your scenario, if you have a Stalwart Poro and Taric, Protector on the same battlefield:

• Stalwart Poro has its own inherent Shield (Shield 1).
• Taric, Protector has an ability that grants Shield to other friendly units at his battlefield (Shield 1).

Because these are two separate instances of the Shield keyword, they stack together. When the Stalwart Poro is a defender, it will have a total of Shield 2 (1 from its own ability + 1 from Taric).