the pictures:

As for your back yard / back garden, a plan view is a good place to start. And, don't bother with computer landscaping programs -- sometimes that's the next question people ask, and the learning curve on those isn't worth the effort -- so use simpel graph paper and pencil. Figure out a scale that is big enough to let you play. Once you have a master copy of the basic scene, you may want to make copies so you can create a couple of drafts.

Then ask yourself, "What do we want to do out there?"
Make a list, and include the regular tasks that you might overlook.
So my back garden list includes:
Garden shed location and orientation,
water faucet / tap
existing concrete patio, sidewalk
compost area
interior / exterior door to lower patio
interior / exterior door from garage to back patio
gate from back to path leading to front garden

But what I also have to think about in some of my arranging is:
sightlines, access to get mower from back garden to front garden, place to create sitting area, and where to put a secret garden.

And, you know, you also have to figure out where the barby goes, right?

Note: I learned to speak Australian, but don't think I ever saw how it was spelled. Oh, the stories I could tell! My poor brother didn't know what a "biro" was until the "master" jerked the ballpoint pen out of his hand and threw it out the window. In the 1970s we were still expected to write with fountain pens.