I haven't used the program you're talking about (I'm assuming you mean Clickteam Fusion 2.5), but what I can tell you is that png is just an image file format, like gif or bmp.  When you import them as a tileset, you'll have to tell the program what size the tiles are (16x16, 32x32, etc), and I don't know how to do that offhand because I've never used it before.

I actually went googling and found a thread on their forum from today (I'm assuming you're the person who posted it).  This answer here looks promising:

"Add an active object to your frame. Double-click it to go to the animation editor. Press Ctrl+O or click the Folder icon to open an existing image. Select the tile map you want to use, click okay, and then in the Import Options screen that comes up, select Import animation and also Sprite sheet and then enter the size of the tiles."

I might be able to be more helpful if I knew what images you're trying to import, but I need a forum account to even view them.   Can you attach them here?

Every painting program, for instance.  Almost any modern program that can open an image can open a png.  It's a very common format.

You linked some specific images in the forum.  I'm asking to see those because I get the feeling from the comments there that you're trying to use sample images instead of actual tiles.  It might help me walk you through the process if I know exactly what it is you're trying to open and how you want to use it.

Use your platform's sub-image or clipped-blit functionality.

If there is no support for subimage functionality you may use the following to break them apart:

http://opengameart.org/forumtopic/graphic-splitter