What you will want to do is decide upon a format for you levels, and then create the editor and have it write your input into a file (either for the level or for the whole game) using the format you have decided. Then when the game loads have it load the current level from that level file(s). Here is an example of what I mean (It won't compile, just for the general idea)
Format
[i]level number, level size x, level size y, coord1, coord2, etc... end a level entry with a ;[/i]
example: 1,2,2,0,1,1,2;
so in the example we would have level 1, it's width is 2, it's height is 2, square x1y1 would contain a 0 block, square x2y1 would contain a 1 block, square x1y2 would contain a 1 block, and square x2y2 would contain a 2 block.
using the format you would write your editor so it would save that information into a text file, either one file per level, or a master file (where the ; or whatever symbol you want comes in handy so when parsing the text file your editor/game can recognize that it has come to the end of a level's data). As to how your editor would get that data from you is entirely up to you. You could write a simple text based entry system
input "what is the name of the level?", level$
input "What is the X dimension of your level?", levelx
input "What is the Y dimension of your level?", levely
*put some code here to figure out how many paired coordinates you will have, using a 2x2 level you would have 4.*
input "What type of block do you want at coordinate x1,y1?", x1y1
input "What type of block do you want at coordinate x1,y2?", x1y2
etc...
Or something more elaborate that uses a drag & drop interface (Example NOT supplied, lol)
In your game you would parse the text file and have it read the information for the level you are loading and load the blocks based on the file.
Am I making myself clear, or just confusing you? lol