Certificates are nice, but people hiring or commissioning you want to see work.
Build something specific
Instead of a website, make a booking page for a local yoga studio. Specific projects are easier to explain and more convincing.
Show the process
Include two or three in-progress images or notes on decisions you made. It shows how you think.
Keep it short
Three strong projects beat ten average ones.
Write one paragraph per project
What was the problem, what did you do, what was the result?
Pick a course with a project at the end, and use it as your first portfolio piece.