This devides the value in D104 by the value in F104. The $ makes the column
reference of F104 a constant. That means if you copy the formula to another
column, the "F" column reference will remain the same.
It divides the value in D104 by that in F104 and gives the same result as
=D104/F104
But if you copy this to a cell to the left (ie if formula is in P1 and you
copy it to Q1) your formula becomes =E104/$F104; note the D changes but the
F does not.
You might see formulas like =D104/$F$104 with a $ on both he column and the
row part. Such a formula leave F and 104 unchanged when copied.
See help under relative and absolute addresses
best wishes