To use the editor, download it and save it to a safe place somewhere on your pc.
Then, i recommend downloading ozzy's download patch for super 14's, although i think the original, and years out of date roster comes with woosaah's editor.
Basically, you can either type the name of a player and it will find them, or select a team and then you can select the players and edit them the same. You just change the values (numbers 0-100) and the others are obvious then click 'save roster'.
If you want to make 'transfers' for a club or national team, you should open up the required team/club from the drop down and the team will be listed, and on the right will be listed all the players in the game who can be picked. You can add players from different countries to different teams, so you could put Lomu in england's team for example.
You do this by clicking on a player name from the left menu and clicking the > button on the editor. This means he is taken off the squad. Do the reverse in the right menu to add players.
The only qualm i have about this editor is that you can get errors when you want to save the new squad you have just changed. Just leave the roster positions as it comes up and try to save. It should then save every player in order and hopefully there are no errors such as 'error with X.XXXX player. May have extraletters after his name. Please fix and try again'