@Shannon430 For this, you will need to choose Conditional Formatting > New Rule > Use a formula...
The formula should be something like =AND($C5=99,$F5>4). The $ in front of C means that it will always look at column C. The row reference (5), should match the starting row that you have in the "Applies to" field. This means that it will apply to the current row. For example, if you set the Applies To to a range of cells in F, like $F$5:$F$100, and the formula is =AND($C5=99,$F5>4), the formula will look at the cells in C and F together on each row, starting with row 5.
It's important to understand how the references work in a formula in Conditional Formatting. A simple example is =A1>100 with an "Applies To" range of $A$1:$B$5. Since the formula refers to A1 (no dollar signs), and the range starts in A1, then the formula would be evaluated for each cell in the range as if you were saying "if my value is greater than 100". If the formula was =$A1>100, it would be like saying "if the value in A on my row is greater than 100". If the formula was =$A$1>100, it would be looking at the value in A1 for all the cells in the range.