Please be aware that A-kasse and Union is not the same thing.
A-kasse is like an insurance - you get Unemployment benefits in case you should loose your job.
A Union helps you with problems that can occur during a job, for instance how to understand your jobcontract, if you get ill, if you are not paid the correct salary, if you get fired without good reason and all these kind of things. So the Union helps you with legal things, and also Unions works on the overall plan to get bettet conditions (e.g. salary) for their members.
You dont need to be member of both A-kasse and Union.
The most danes who works are member of an A-kasse, but not all are member of an Union.
It is easy to sign up with an A-kasse - everything now a days are done online. We have a little guide on how to do it on our website:
If you need further help, then please post your question in our Q&A forum