Help in adding celestial bodies.

@sflanker Thank you very much and sorry for that mistake. It was actually celestial body.

Assuming that when you said "how to add crafts to my stock system" you actually meant Planets/Moons. In planet studio you select the celestial body around which your new planet/moon will orbit, then in the "Map View" panel click the button that looks like a target reticle (strange icon choice, but the tool tip says "Add new planet"). This will prompt you to select a previously saved planetary body and place it in orbit around the currently selected body. You can then set the new celestial body's orbital parameters.

If you actually did mean "craft." Then I don't really understand the question. Open a craft, click the blue play button, select Launch Craft. If you want to start from a different location, use the Flight Menu and click Relaunch. This will let you select a previously saved location. There's no way to select an arbitrary location to launch a craft*. So if you want to get there you've gotta fly there.

* Technically you can do this in planet studio as well, although initial launch locations must be on the surface of the planet, not in orbit.