Don't try to level the slope unless you plan to add retaining walls. To plant on a slope, hollow out a spot for a plant (use the extra soil on the outside of the little shelf you have created) and plant. Use drip so you don't cause erosion. If you just want one type of plant, Junipers work well but, as you didn't list a location or add any photos, just a guess.
I found a drawing to show what I mean:
https://www.pinterest.com/pin/...
I hope this helps.