There are two kinds: 1. An addition to the constitution. The parlament then has to implement that into law. 2. A referendum on a law that has been passed by p

There are two kinds: 1. An addition to the constitution. The parlament then has to implement that into law. 2. A referendum on a law that has been passed by parlament. This allows the citizens to revert a parlamentary decision. There is no way to vote on a new law directly. However you can get close by just having a very detailed constitutional change that doesn't leave a lot of options for implementation open.