Hey Franssen,
seems like you're missing a few modules.. An envelope generator solely generates a signal. It can't process audio like an amplifier. To use the doepfer adsr correctly you need an exponential voltage controlled amplifier, or vca for short. The vco's output goes into the vca's input. The envelope's main output 'opens' the vca and makes the audio signal form the vco louder and quiter following the envelope. Secondly you're going to need a voltage controlled filter or lowpass gate. A lowpass gate already has a vca and envelope integrated, but your setup really needs a nice analog filter. Doepfer has loads of great sounding filters, but if you're really into eurorack modular and have some cash to spare, get Intellijel's Polaris VCF. This vcf is a very, very versatile filter with an integrated phaser circuit!
Also, go on the internet and take a very good look at synthesizer signal paths. That is quite fundamental knowledge to even understand a simple modular patch. There is a guy on youtube who can explain all of this, and more, very well and erudite! Here's the link to his tutorial series:
So here's your shopping list: -a voltage controlled amplifier (VCA)
-a voltage controlled filter (VCF)
don't forget some good patch cables!!
I hope this'll help you as an introduction in the very fascinating world of eurorack modular! And as always, keep wiggling!