That's a huge question that this forum is all about. I suggest you start by deciding what kind of potting mix you want to use. The long-running discussion called Container Soils -- Water Movement & Retention is a good place to start if you're willing to take a little time to learn the basics. You can read that by clicking this link. After that, decide what plants you want to grow and research their specific needs.

One thing to consider is that growing anything from seed is going to be a lot harder than starting with young plants. You might want to start small and learn as you go.

If you're going to buy ready-made mixes, then just make sure you choose he ones called "potting mix".

There are many plants that do just fine by planting the seed in the pot, but really, if you have a list of plants you were interested in, we could give a better suggestion about how to go about it. For example, things like are you doing veggies or flowers, annuals or perennials, etc

After figuring out the potting soil, there are few questions:

!- What are you going to grow ?
2- What kind/ size containers do you have ?
3- How many containers/plants are there ?