I'm looking for resources to understand the fundamentals of delta-epsilon proofs

Question

Here are some examples of proofs I struggle with:

1. Consider the sequence {$15^2+2√+3$} $\lim\limits_{→∞} 15^2+2√+3$=_____

2. Let $()=2^2−4+5$. Use the − definition to prove that $\lim\limits_{ \to -1} 2^2−4+5≠8$.

I'm struggling with how to solve these proofs in general, my textbook hasn't been great.