Stream/waterfall

I love the rocks, they are pretty and have nice colours. I can see your concrete sides, and I think you want to plant something along the edge which will hang over. Moss I think only grows in shady areas and by the looks of your pic these are in full sun. Perhaps a ground cover of some kind which grows fast. I don't know any names of them but I used to have some, also with pink or mauve flowers and they grew over my rock wall quite speedy. You'll have to buy them at the nursery I think, so why not ask them. Also, you don't want them to start running over your lawn ( the creepers ), lol. Maybe there is a fern which can stand full sun too, that would look nice.

Marguerite is right - moss needs cool, damp and shady conditions to grow. Ferns also need shade - I can't think of any that enjoy sunny places. Why not more grasses for now, like the lovely one in the photo - is it a Stipa? Then try low-growing plants like Creeping Jenny, small yellow flowers - it's 'Lysimachia nummulaaaria 'Aurea' - or 'Convululus sabatius' mauve flowers, or Persicaria affinis . In the spring there's lots of choice - Aubrieta, Saponaria ocymoides, Iberis sempervirens, Alyssum saxatile, Phlox subulata etc. Once you have these established your stream will look so pretty!

PUT SOME GRITTY SOIL INBETWEEN YOUR ROCKS. PLANT NEPETA - LAMIUM(WHITE NANCY), CAMPANULA, mERCADONIA. WATER REGULARLY FOR FIRST MONTH UNTIL IT ALL GETS ESTABLISHED.