Finder opens new window each time
There are many things that could be going wrong here. First of all, make sure that when you navigate to Finder > Preferences > General, the option "Always open folders in a new window" is unchecked. If not, there are many solutions to your problem listed below:


Naviate to View > Show Toolbar
Navigate to View > as List, as Columns, or as Cover Flow
Get TotalFinder (http://totalfinder.binaryage.com/), which adds many more settings to Finder


Good luck!