A formula is a sentence containing variables. Formulas often describe a relation between those variables, but not always.
Formulas often look like an equation, i.e. a sentence with an equals sign.
If a formula describes a relation between two variables, you can draw a corresponding
graph. First, you make a table. Next you draw the points in a coordinate system and
connect them.
In practice, formulas often describe relationships between quantities. Those quantities are represented by a variable, a letter which corresponds to the
name of the quantitiy used.
A quantity is measured in units.
The formula $A={z}^{2}$ is an equation defining the relation between the variables $A$ and $z$. You can make the corresponding table and plot the corresponding graph.
The formula $2t+40=300$ gives information about the unknown $t$. The solution to this equation is $t=130$, for $2\cdot 130+40=300$.
The formula ${(x+3)}^{2}={x}^{2}+6x+9$ is a calculation rule and is valid for all $x$.