Assuming you are talking about Google Navigation, there are two ways to accomplish this.
1) on your phone, open the Maps app instead of the Navigation app. Browse to the location of interest. Long press the map at the desired location. Click the right facing gray arrow to the right of the resulting address that pops up from your long click. At the very top right of the screen, press the gray star. The star will turn yellow and when it does you've just created a starred favorite.
2) If you would like more organization than that, such as organizing things by categories, etc. then go to Google Maps on the web. Click on My Places, then on Maps. Click on Create Map. Give it a name (I.e., Family or Restaurants or Vacation), pick whether you want it shared with the public or private, then hit Save. Go to anywhere on the map. Right click anywhere you desire. Select What's Here. Over at the left, select the most applicable item and select Save to Map. Pick the desired map you created or even select Create A New Map, then hit Save. You can then go back into My Places on the web and edit this with descriptive names, more text, etc to your liking. Now go back to your phone. Open the Maps app. Click the layers icon at the upper right. Select My Maps. Pick the Map you created. In the future, when you edit these on the web, they are synchronized to your phone through MyMaps.
Once you go the MyMaps way, right now, there is no way to edit or add items from your phone to MyMaps categories. You can only add Starred Favorites on your phone. What I do is mark a starred favorite on my phone, then go back to the web at a later time and add it to MyMaps then remove it from starred favorites. Hope that helps.
