Do a lot of reading on these boards and ask any other questions that you may have. In your research you will find that swinging has a trillion facets and at the core of everything, swinging is about taking empowerment of your sexuality and pursuing your sexual interests as a couple.
If you find it sexually stimulating and feel that it would add some extra sexual energy into your relationship as a couple to watch another couple make love then pursue that. All you have to do is ask in a polite and respectfull manner and at that point they can either say yes or no as that is their perogative as a sexually empowered couple. It may turn them on to be watched so everyone comes out a winner. See how this works?
There really are no "these partys." People do what they want to do and everyone can pursue their own interests. My advice is to keep talking about and do a lot of research. If you want to feed the voyuer flames some more maybe rent some XXX movies and watch together. My recommendation would be to find some actual homemade movies of actual swingers rather than garden variety commercial Hollywood porn movies with paid actors that are all surgucally modified and following a script. If you watch real people doing what real people really do it will be a lot more erotic even if there are some love handles, stretchmarks and receding hairlines.
The most important thing is to keep talking and keep sharing your thoughts and fantasies.