To make avocados grow you need to do 4 things:
1. Plant a Seedling
2. Graft the seedling (Here's why:    • Should I Graft My Avocado Tree?  )
3. Plant in the ground in the right climate zone
4. Pollinate your trees

This video tells you everything you need to know about the 4 elements. (I accidentally reversed afternoon and morning on the pollination vid but the concept remains the same you need a mix)

If you want to buy a tree or some clippings (scion) to try your hand at grafting go to: https://www.guacfarm.com