Assume the new unit is NewUnit1, make the procedure available to other units by putting its declaration before the implementation section:
unit NewUnit1;
interface
..
//Here you can make a procedure visible to other units when they use this unit
procedure NewProcedure1(...);
..
implementation
//This procedure is visible outside this unit
procedure NewProcedure1(...);
begin
...
end;
//This procedure is NOT visible outside this unit
procedure NewProcedure2(...);
begin
...
end;
Add the newly created unit to the uses section of the main unit:
uses
..., NewUnit1;
call the procedure in your code:
...
NewProcedure1(...);
...
Notice that NewProcedure2 is not visible. Any thing you put after implementation is not visible outside that unit