importing tiles in Basecamp

For my next bike trip I have selected the tiles I need for the area I am cycling. Managed to get all that on the computer. However I am not able to get them imported into Basecamp.

I have installed Combiner but do not get on the 2nd screen a selection of files to choose from or am I able to drag files into the selection box.

Would really love some step by step help to get my files visible in Basecamp.

Look here