The scifi category is a bit different from others. it utilizes patch mode on a single quad face. Therefore, during face selection, make sure it is generally a square shaped, so that the script can reduce it to a single quad face. if all things failed, you can always select a single quad face to start and scale it up. 

1. choose a category. 

2. make a mesh of your liking and rename it something unique. 

3. take a screenshot or render of the object, name it same as object name in jpg format.

4. save the blend file same name as the object name.

5. put the blender file and picture into the relevant folder and press refresh preview in addon preference.

you can now use it every time blender is open.

make sure both the base object and cutter objects have adequate mesh density to bend.

In Blender 4.2 or above. make sure download and enable the tissue addon from Blender Extension Platform within Blender or from its site. in earlier versions, tissue addon is included with blender, simply enable it.

also check the custom folder name, make sure it is a valid direct path not relative path and make sure there are no empty space either. if there are couple of empty spaces, it is treated as an invalid folder path and can not get any preview images.

1. create the element. if it is not facing up, apply transform-rotation

2. create base, also apply transform if not already. then first select the element mesh and lastly the base mesh, click add element. you can also change how the normal is aligned. please note, it will distribute on all faces, delete faces that are not required.

3. after "add element", the base mesh and element mesh are duplicated, they are child objects and hidden.

unhide them and you can modify the overall shape. press refresh to update the change.