hi , it is a nice backyard that you have , i widh that i have a small one like it , it's okay it is easy to create a small garden for you , first you need to do a small research about you weather and what kind of plant growth there , so there is a lot of plant that doesn;t need a maintenance but maybe water the first 2 years in summer , so as i see you have a 5 stairs that we can benefit to do a small stream next to it . it's easy and not expensive ,you can plant some vegetables it will help you to eat a fresh food like tomatoes it is easy to growth it , you can put a on the fence some trees it will extend and will make it beautifull