help please with my desert star

Cathie

That looks like a Natal plum (Carissa macrocarpa), though it's not the best picture. It should be planted in a gritty, fast draining bonsai mix rather than peaty potting soil that stays wet for days, and once that's done, you allow the top 1/5 or so of the mix to become dry before watering again - and if in doubt (depending on how the plant reacts) wait another day. Keep it in full sun all day, remembering it's a tropical and so should live indoors for the winter. If it seems healthy after a few weeks or so, you could cut back the long branches to just a few pairs of leaves each, and should see more foliage grow out eventually. In the early spring, you could choose which more major branches to keep for your 'design' and which to prune away - but you might also just let it grow for a few years until you have a better idea. You also want to check the rootball later in the year to be sure roots are not circling it to any extent - and that might be the time to repot into a better soil mix mentioned above. If you do that, you'll have to water less frequently til then, and not if the top inch is still damp from the previous watering.