When Intent Mattered Most: Express and Implied Intent Confusion

Yaar, samajh nahi aaya! I've been struggling with sections 30 and 19 of the Contract Act. I get that both talk about intention, but somehow my notes got all jumbled up. Section 19 - 'If an Apparent Authority holds himself out as Agent...' - it says intention of the Principal matters. But then section 30 - 'Where, at the desire of the Principal, the Agent does an act...' - it seems to also depend on intention of the Agent. I'm all confused, yaar. Is it one or the other? Please help me clear this doubt.

Can someone explain to me, how do we decide which intention matters - that of the Principal or the Agent? And in what situations? I've read and re-read sections but somehow, my understanding still doesn't make it clear. Need some guidance here, guys.