i need a bpm counter witch send a message if a tempo of incoming Audiosignal changes. Have anyone an idee?
It sounds like you're really new to Max MSP and audio processing in general so I really can't stress the importance of understanding how audio processing works in general and how much you'll learn just going through all the built in tutorials in Max. Beat detection is a pretty complex thing though, take a look at how even pro softwares like Ableton and Traktor have trouble tracking beats sometimes, and they have people who've worked on their algorithms for years.
There are a number of ways you can do an implementation in Max, it really depends how much time you want to spend and how complex you want to make it. The simplest would be to put a low pass filter on your track (if you're measuring against the kick drum), and then get the level of the signal, then set a numeric threshold that triggers when the level goes over a certain value, and have that connected to a bang that is connected to a tap tempo calculation. You can find an example of a tap tempo at this link: https://cycling74.com/forums/topic/tap-tempo-2/
Another option is to use the beat~ object found here: http://web.media.mit.edu/~tristan/maxmsp.html
For the message sending side of things, who are you sending a message to? You can use udpsend to send messages over the network, you can send midi out values, or just use the built in send and receive objects if you're just sending data around in Max.