nodesuka のですが

First of all, "no desu ga" is written "のですが" in japanese, so in alphabet, it should be "nodesuga". No spaces. 

This expression could be used for a sentence of contrast. 
For example, "I want to go, but I sleep today." 
⇒行きたいのですが、きょうはねます。 
　Ikitai "nodesuga"、kyouha namasu。 
In this case, "nodesuga" was used as "but". 

There is also another type of sentence which doesn't have the last half part of sentence. 
⇒行きたいのですが・・・ 
　Ikitai"nodesuga".....(end) 
This is a sentence that the speaker is "indicating" that the speaker has a negative condition from the first part of sentence. So that a listener would be able to "guess" that she/he can not go.