Let's explore the fascinating world of functions in Algebra I! 🌟

1. What is a Function?
   Think of a function as a special machine. You give it an input (often called $x$), and it gives you an output (which we write as $f(x)$).

2. Finding the Function Rule:
   Check out the function's equation! If the function is written as $f(x) = 2x + 3$, it tells you how to change your input into an output.

3. Plugging in the Input:
   To find the output for a certain input, you just replace the $x$ with that number. For example, to find $f(4)$, you do this:
   $f(4) = 2(4) + 3$
   That becomes $8 + 3$, and the answer is $11$!

4. Try Again!:
   Keep using different inputs to see how the outputs change. It’s a fun way to learn about functions! 🎉