buy the seeds and follow the instructions. geraniums and pelargoniums [often mis named geraniums] are easy to grow.

Sow now, but keep them in warmth, I've just sown mine and they are on a south facing window ledge above a radiator. don't overwater them and on really warm sunny days protect the seedlings from the sun with white papr placed to shade them. I have never failed to get results this way.