Hi Radek,
Your best options are to check The Seed Site(link below,) and to do searches of this forum. After searching the Seed Site and this forum, if you do not find an answer, please post a question to this forum.
It is also good in general to find the Latin name of the plant you are trying to save seeds of. You will get better search results that way.
Remy

Here is a link that might be useful: The Seed Site.

There's also the FAQ on the main page of this forum. Good basics.

(The Seed Site rocks! bookmark it.)

You mention you are very new to gardening. Hopefully you realize that several of your plants are perennials and should return next year as long as you do not pull the roots out of the ground at the end of the season. Of course you can also save seeds from them and grow even more. But even if the seed saving and growing from seed fails, you should still have several returning plants that are even larger next year and might be suitable for dividing.

Sunflowers are very simple if you can beat the birds to the seeds. The center of the flower is the seed head and once the flower dies the seeds are ready to harvest. Just pluck the head from the stem and turn it over on a sheet of paper and let it dry. As it dries it will drop the seeds onto the paper. To get any left in just run your hand across them.

You might want to put a net over the flower to stop the birds.

Purple Coneflower is another where the seed head is pretty easy to identify. It is the cone shape at the center of the flower. Again let the flower die and then pluck it. Let it dry in a little bowl or container and once it is dry pluck out the leaves and behind them you will find the seeds.

Enjoy harvesting your seeds.

There are quite a few seed saving articles at one of my blogs if you would like to visit it. It is called Garden, Tools & Seed Shack. I don't sell anything there--just organic gardening tips and advice with lots of pictures. It is free and no sign in required, just good reading!

Seed saving is really fun and it's not hard to learn the basics. I joined a seed saving group in my area 2 years ago and have learned SO much from other members. So, search out some of those in your area to learn from those who do it.

Look up the scientific names for your flowers online and whether they are annuals or perennials. Annuals have to be replanted "annually" or each year. Perennials will come back on their own every year as long as weather conditions don't kill them off.

Here is a link that might be useful: Garden, Tools and Seed Shack Blog

Hey thanks everyone for the great leads and suggestions. I have had some good luck so far. Four O'clock, Mexican Sunflower, Coneflowers and Daisey I am good to go but I am having problems finding the seeds on the Evolvus and can't find much info on the net about it. The flower only opens it seems in the morning/early afternoon and closes up again so trying to find the seeds on these little guys have proven hard so far. My wife loves them so I would like to get them going for her again.

Another good news is after waiting all summer our Morning Glories bloomed today. Very exciting.