Question: “How do I send posts to only certain groups of people?”
Answer: see Q&A Friend List for the first step in this process. Facebook allow remarkable flexibility in your privacy settings for individual posts. After setting up friend lists you can include or exclude groups and individuals so your posts go only to those you want them to go to.
On your News Feed page, click into the status box. Now below the box next to the Share button an icon of a lock appears. Hovering over that lock will show you what your default setting is for sharing. Click on the lock to change your settings. Then highlight Custom and choose edit.
Use Make this visible to: these people to choose a certain group or groups from your friend lists to show the post to. Click on the drop down arrow and then specific people. Begin typing name of friend or list. Select the list when it appears.
To hide the post from a person or group of people repeat the process in the Hide this from these people: box. Then click save setting. Your setting is good for the next post. To keep the setting for all posts you need to check the box next to Make this my default setting.