Imagine you have tiles at home with a size of 10in x 10in. With slicer you can slice your image in different parts, to create bigger images at the end.
So you need to prepare your image on imag-r.com and resize your image for example to 20in x 20in. Then you upload it here on Slicer and choose by Numbers 2/2.
You will now get 4 tiles, with 10in x 10in each. The 4 files will be downloaded in a zip file.