I know (at least I think I do) that an estimator is a random variable and can be expressed as a function of random variables.
An interval is a range of values.
I can't really explain what an interval estimator is.
It's homework, so I would appreciate a really simplified explanation (if there is one) about an interval estimator.
Your comment is along the right lines. Following @StubornAtom's comment, one simple example of a 'confidence interval' is as shown below. A confidence interval is one kind of interval estimator.
If $X_1, X_2, \dots, X_n$ are a random sample from $\mathsf{Norm}(\mu, \sigma),$ then $\bar X = \frac 1n \sum_{i=1}^n X_i \sim \mathsf{Norm}(\mu, \sigma/\sqrt{n}).$ Thus, for known $\sigma,$ we have
$$0.95 = P\left(-1.96 \le \frac{\bar X - \mu}{\sigma/\sqrt{n}} \le 1.96\right) = \cdots \\ = P(\bar X-1.96\sigma/\sqrt{n} \le\mu \le \bar X+1.96\sigma/\sqrt{n}),$$ so that a 95% confidence interval for $\mu$ is of the form $\bar X \pm 1.96\sigma/\sqrt{n}.$
When $\sigma$ is unknown and estimated by the sample standard deviation $S,$ a similar interval based on Student's t distribution is used to make a CI for $\mu.$ Look in your textbook or class notes for that.