Soil and compost is key to growing healthy plants. Soil is the top layer of the land that supports plant growth. Most soils are composed of a combination of different proportions of sand, silt, and clay.
In general, plants thrive best in rich, sandy loam. Of course, there are specific needs for some plants. For example, some may require a greater percentage of sand for effective drainage. Generally, I have found that if I consider where the plant grows natively, and mimic their natural environment as much as possible, the plant will do well.
The best thing you can do for any soil is amend it with compost. Compost consists of broken down plant matter and provides the nutrients for the next cycle of life.
I am a big fan of Dr Earth products. If you are unsure of your soil, you can opt to purchase a bag of Dr Earth all-purpose soil to get started. It also already contains worm compost.