A narrow spot in the geyser tube or plumbing system makes it difficult for the water to flow, causing heat to build up. The result is water turning to steam in the form of an explosion. . A spring usually has lower temperatures. It can be just a pool where water flows. It can be cool, warm or tepid.
Springs can be clear or muddy.
A fumarole has less water than a spring. Basically, if all that a person can see on the surface is water vapor and other gases, then it's a fumarole. A mud pot is appropriately named. With so little water, the clays keep accumulating. Yellowstone's geysers have been here for a long, long time.