The Survivors' camp is a zone that is unlocked during main questline; other than when you first encounter it during the quest, this map is safe and has no infecteds. Upon entering each time, you will randomly be put in a house; while the location may change, the things you place do not. Once the camp is unlocked, you will spawn here when you die.
In your first encounter of the survivor's camp after talking to Gary Anders, you are taken to the Camp Entrance and are tasked with killing the five infected planted near the gates. This is the only time you will ever be in the Camp Entrance, as you have already gotten to the Survivor's camp afterwards.
To build anything in your camp, you must obtain resources, which can be done by salvaging items at your pantry. If it the first time you salvage an item with a recipe/way to build it, that recipe will be added to your known recipes.
Buildings are structures you can build in your area once you have obtained the blueprints. You only start out with two buildings that you need to construct the rest: the Stock (for storing resources), and the blueprints table (for constructing buildings from blueprints you find).
You can move place structure by hold ⇧ Shift and clicking it, and can rotate a building you're moving by pressing R.
Salvage your items and get basic resources for your camp. You may get some of these basic resources as it depends on the item.
Click to enlarge. Map image provided by Verdecon.