I have to make a presentation run by PDFlatex. But I want to draw a picture in it with the Tikz package. How can I manage this?
Have a look at the great TikZ example gallery. You would find more than hundred examples in different categories with the complete source code. Using examples makes starting easier.
On your computer, you can open the very extensive TikZ manual by typing
Further you might find interesting:
Or video tutorials:
More resources are listed on http://www.texample.net/tikz/.
Start by reading and stepping through the graduated exercises in the wonderful TikZ and PGF manual that comes with the package, downloadable from CTAN. Then consider whether to use the beamer package as the container for your TikZ components. From there, you'll be able to ask more directed questions about what to do. Best of luck!