There are many ways to build your EndNote library - one way is to enter your references manually. You may also need to correct or complete the data in references which have been imported.
There is a sample library in the EndNote Examples folder within the EN program folder on Windows or within the EN application folder in Applications on a Mac - you can use this to see how references should be entered in an EN library.
The Writing Centre at the University of Adelaide has produced Referencing Guides to some of the common styles used at this University. You can see examples of how these references should be entered into an EndNote library to produce the required bibliography in that style. Refer to Styles in this guide.