The tools to design your landscape depend on how accurate you want it to be. You could use simple objects like triangles or other basic shapes like in this tip or this video .
If you want go further, you'll probably have to use some other software like Cecilia shows here .

It's never too late to ...

Related questions are;

Is it possible to add a level below Level 0?

Can level 3 have a lower elevation than level 0, if you forgot to put in a lower level?

I have created a reasonable facsimile of the exterior of my home. It has 3 levels. Now I need to add driveways, retaining walls all with elevation changes which are below the height of level 0.

How can I accomplish this?

Tutorials are great, just point me to them.

I am new to SH3D. I am looking for tutorials, explanations or any ol' help to implement a a drawing which I was able to cobble together in v14 of Punch Home Design. I am looking for a new tool because of my inability to make that program do what I want.

My goal is to do exterior remodeling ...