Step1: Find domain of $f(x)=5\cdot8^x$
Exponential functions accept all real $x$, so domain is all real numbers.
Step2: Find range of $f(x)=5\cdot8^x$
$8^x>0$ for all real $x$, so $5\cdot8^x>0$. Range is $\{y \mid y>0\}$.
Step3: Confirm y-intercept
Set $x=0$: $f(0)=5\cdot8^0=5\cdot1=5$.
Step4: Confirm horizontal asymptote
As $x\to-\infty$, $8^x\to0$, so $f(x)\to0$. Asymptote is $y=0$.
Step5: Describe end behavior
As $x\to-\infty$, $8^x\to0$, so $f(x)\to0$. As $x\to\infty$, $8^x\to\infty$, so $f(x)\to\infty$.