They're called ear clamps, they start out life looking like this:
To attach them, the band with the holes is hooked up as tightly as ossible so those "fingers" poke through the holes, and then a tool like this:
Is used to squeeze the lump in the clip and reduce the circumference, squeezing the clip together. It ends up looking more like the sketched black outline:
At a push they can be re-used: bend the small "fingers" straight (on your lip it looks like you'll only need to do the longest one; the others don't hook over the band) by pushing a small flat bladed screwdriver in (red arrow actions) and levering upwards, then separate the clip by pushing the screwdriver in between the bands (blue arrow actions) and lever upwards again. Use pliers to pull the clip band up off the fingers:
Once you've got it off you'll need to use pliers to carefully bend the lump back to close to what it looked like as new (so the clip circumference is bigger), but it'll make your life easier to leave the fingers straight.
For refitting, fit the clip, then bend the fingers down, then use nail-puller style pliers (pictured above) to squash the lump again, reducing the circumference
You can really only do this a limited number of times as the clip will be weakened every time it is bent, but for this application (low pressure water hose) reusing it a couple of times will be possible