Creating addons is hard, often overwhelming work. This document will provide you with a jump-start guide to addon creation, with an emphasis on “here is where to find more information”, rather than rewriting everything here.
You should join the following discord servers:
The best place to start is probably the Minecraft Bedrock Beginners Guide. You should also bookmark the Minecraft Bedrock Documentation. After that, your best bet is to just try things! Download the vanilla Behavior Pack and Resource Pack. Poke around. Try changing things.
You will need to debug your entity. The troubleshooting page can be useful.