A soil amendment is any material added to a soil to improve its physical properties, such as water retention, permeability, water infiltration, drainage, aeration and structure. The goal is to provide a better environment for roots.
To learn more details about soil amendments, read more from an Colorado State article.
You might also consider having your tested before adding soil amendments. There are several kits that can be purchased.
After testing your soil, you will have a good understanding of the types of nutrients needed for your soil to thrive.
Remember that over time, some soil nutrients get used up by plants. You will need to enhance your soil periodically with additional nutrients.