@Pacogssl Associations are one of the big mysteries of Z-Wave! Personally, I am not a huge fan of Associations (in practise rather than theory) - mainly because it is easy to lose track of what is happing with your Z-Wave network and you lose a lot of “granular control” - my best advice if you would like to persevere with Associations is to keep a record somewhere written down!
Actually assigning an Association in Homey is rather simple…
- First, make a note of the “Node ID” for the device you would like to control (Device Settings > Node Information)…
- Next, open the Settings for the sensor you would like to “Associate” with the device above (Device Settings > Associations) and enter the “Node ID” from above…
WARNING: We do not want to remove “Node ID 1” at any stage - this is Homey! Also, Association “Groups” can change between devices. For the example above, I am using an Aeotec Door/Window Sensor 6 - this only has one Association Group - to which we can add up to 5 devices - don’t forget, Homey will take up one of these slots - each Node ID should be separated by a comma ( i.e. 1,72,56 ).
Other devices will have multiple Association Groups, some of which can only have a single Node ID - and are used for various Association tasks - Hovering over the “i” next to each Association field will provide more details on the various Association Groups for each device in Homey.
Here is a really well written overview of Z-Wave Associations.
Final comment… Z-Wave Associations are a difficult beast to master and somewhat complex… I caution to use them sparingly. There are a few instances where they can be very useful (e.g. a Z-Wave Smoke Detector “Associated” with emergency exit lighting - so even if your Z-Wave controller becomes inoperable, these two devices will still communicate) - but to be honest, I have never really found much use for them - again, if you do use Associations, keep track of them somewhere!
I hope this helps 
