Sorry, my question is little dumn , but I am new in this. How do I frost a cake with chocolate ganache? do I have to mix the ganache before I put on the cake or just put it liquied direc on the cake. Do I have to put butter cream before the ganache or how it work ..

You can pour or wait til it sets and pipe like basket weave.

Like Moydear mentioned you can pour or pipe.
If your ganache is not quite pourable anymore but not yet set, you can try to use a spatula.
You can check out my photos. I did this for an egg at easter, then I found out from one of the posts, that you could warm up a spatula and even it out. I tried it with the leftover ganache and it worked out really nice. I did it on a muffin so I did not take a pic. But it worked great.

Good Luck.

Do you frost the cake first with buttercream?

If I am piping I just crumb coat and then pipe with no butter cream.

If you are going to pour I do not, if you use a spatula just like buttercream, you should.

Good Luck.

I like to pour it over buttercream. It's really yummy to have two layers of good stuff

Ganache is my friend! I like to chill and then whip it and use it as a filling. It is great in the middle of a hazelnut bownie. Sometimes I just eat it out of the bowl. Maybe I should make some tomorrow

I have a very close friend who called me and asked me to make her a batch because she was having a bad day. Of course I made a little extra after all my day was kind of rough I am making my friends son's b-day cake this weekend, so I bet you can guess what the filling will be

Thank you ladys for all your tips.. it help.!!