The blob as a whole has a threshold value. Everywhere in space where the sum of all the components' strengths equals this threshold is on the surface of the blob. Places where the sum is greater than the threshold are inside the blob. A newly-created blob has a threshold of 30 and a single component whose strength is 100 . The blob looks like a sphere somewhat smaller than the component.
Interesting things happen where the components overlap.
Adding together smoothly changing force fields results in a smoothly blended transition between the components. You can give a component a negative strength if you want. Such a component will make a dent in its neighbor instead attracting it and blending with it. You form interesting blobs by lumping together positive components and carving them away with negative components. In the lower-left corner of the Blob Editor are three text entry fields and a Refresh button.