What is the difference between a condensed structural formula and a structural formula?

A structural formula uses lines to show how the bonds between the atoms. A condensed structural omits most or all the bonds.
Structural Formula
A structural formula tells us which atoms are in a molecule. It also tells us how those atoms connect to one another.
There are different types of structural formula. The simplest structural formula tells us which atoms connect to which.
Below are the structural formulas of ethane, propane and ethanol.
Condensed Structural Formula
A condensed structural formula is a system of writing organic structures in a line of text. It shows all atoms, but omits the vertical bonds and most or all the horizontal bonds.
The condensed structural formulas of ethane, propane, and ethanol are
CH₃CH₃, CH₃CH₂CH₃, and CH₃CH₂OH
It uses parentheses to show that polyatomic groups within a formula are attached to the nearest non-hydrogen atom on the left.
So the condensed structural formula of propan-2-ol is CH₃CH(OH)CH₃.
It also uses parentheses to show that polyatomic groups at the beginning of a formula are attached to atom on the right.
So we could also write the condensed structural formula of propan-2-ol as (CH₃)₂CHOH.
And we could write the condensed structural formula of hexane as CH₃CH₂CH₂CH₂CH₂CH₃ or CH₃(CH₂)₄CH₃.