OK, besides you need to choose File/Import project into Workspace, there are some things that can confuse even an experienced user.
You have to add SWT libraries to the build path. Open Project/Properties dialog, then select “Java Build Path” (at left) and “Libraries” tag. You should see a tree item “swt.jar”. Expand it and click where is “Native Library Location”, then push “edit” and add all the SWT native libraries (*.dll or *.so files). Other way is adding “-Djava.library.path=/path_to_libraries” at “Arguments → VM Arguments” of eclipse “Run” dialog.
You should know that if you are using SWT version 3.3 and above, native libraries are included inside the jar file, so there is no need for explicit native libraries including.