For example how to say 3.5 (three point five)? Is it like Deutsch drei komma fünf?
Swiss people will always say a "Komma" when it comes to exact decimal numbers. Just with the relevant dialect.
2.3 can be "zwoi komma drüü" or "zwei komma drei" (or similar) depending on where you are. But the "Komma" never changes
You can either write a comma or a point. Comma is what is usually taught in schools whereas point is often used in print or computers.
One thing to note: for the .5 decimal it's very common to use "ehalb" (ein halbes) if you're talking about it in a non-scientific context. (Prices, hours etc).
1.5 is also special as it can be either "einehalb" or "anderthalb".
Anything else is again used regularily (your example of 3.5 is "dreiehalb" or "drüüehalb")