For example, the Fischer projection of D-gulose is
To convert the Fischer projection to a bond line formula you just draw a zig-zag line of six carbon atoms.
Then you put an aldehyde group at #"C-1"# and #"OH"# groups on each of the other five carbon atoms.
Note that the bond line formula gives no stereochemical information.
It shows only which atoms are connected to the other atoms.
The structure above could represent any of the fifteen stereoisomers of D-gulose.