algorithmic modeling for Rhino
If you are trying to learn GH through a video tutorial and can read a components name on the screen but don't know where to find it then you can invoke the Create Facility by double clicking on the Canvas or using the shortcut key F4. Type the name into the box that appears and you will be presented with a list of likely candidates.
Once you have found the most likely culprit you can selected it from the list and place it on the Canvas.
Both Icon and Text
If you have downloaded someone else's definition and are wondering where you can get a component from on the Ribbon then provided you have the GH window wide enough to display all components [EDIT: This is now capable of showing any component in the dropdown menus] then you can hold down Ctrl+Alt and click on the component. A series of arrows should indicate the Tab and the Icon you are looking for.
If you can see the Icon but don't know the name then things are a little trickier but not all is lost because with a little bit of detective work Help is at hand......literally. On the Help Menu you can choose to export Help...
This will create a series of off-line web pages, one of which is a summary page titled "Grasshopper(X.X.XXXX) Help Summary" which will list all of the current components grouped in their Ribbon Tabs. With a bit if guess work you can narrow it down to certain categories like Surface or Curve then simply browse down the list.
[EDIT: There is also a VB Script component that David has created to produce an image of all your components]
If all else fails post a screen shot of the component in question in the discussion forum and with in the hour if not minutes you will probably have an answer.