You can celebrate Juneteenth the way that you want to. There are some people who even create parties for it. This will allow them to celebrate with other people who are also happy that slavery is already over. It is best if you would create an event wherein everyone can participate in. You can let people bring food that is related to Juneteenth and you can all eat and bond together.
Some would even discuss some of the things that may have occurred at that time. It will depend on you how you would celebrate it. The important thing is that you will remember why it is being celebrated.