If the APIs are well documented, it is a breeze. You need the function prototype which is found in header files and in the function definitions in good API documentation. The prototype contains the name of the function and the calling syntax, including the type specifications for the input parameters. You use the prototype to configure the function call. Plop down the call library function, then right click on it and pull down to configure. Put in the path to the .dll that contains the function you want to use, then fill in the function name and parameter details. Be sure to note if you are passing pointers or values in the configuration. The problem I find is that the manufacturers do not always provide adequate documentation to know which functions to call and when to call them. Extremely clever and persistent individuals can figure it out, but good documentation saves hours, days, weeks, etc.
Now, if their code is provided as an active X control or a COM object, you can do a lot without documentation, because so much of the beast reveals itself to you. You put this code in an ActiveX container. Then you set properties and invoke methods using the ActiveX functions. It tells you what functions are available. The info at the following link is indispensible: http://zone.ni.com/devzone/devzone.nsf/webcategories/69AC4D47BD54298A86256AB7006AB23C?opendocument&node=DZ53009_US
