Help building a floating menu plugin

Hi all, new here - came inquire about resources on building custom blocks. Is there a go-to article someone can point me to for building a custom block and/or something like a floating menu? I'm familiar with the process for creating themes but still unsure about UI plugins or extensions. Thank you very much!

You want to build a custom plugin, or to build a simple floating menu?

If custom plugin, you try contacting SQSPTHEMES, Squarewebsites, SQSMods, they develops some great plugins, so I think they can give you a good direction to get start.