Hi Jean Claude
I'm just going through this forum and saw your post. I'd like to help with that if I can. This is just one way.
First you need a Gmail account (firstname.lastname@example.org)
2. Log in
3. While logged in, go the the address bar and type - google.com/adsense - you should see the Adsense logo at top
4. Click "My ads"
5. Click "New ad unit"
6. Go through that and play with designing your ad units.
7. Do a few ads of different sizes. Try and match the design to your blog so it looks good on your blog. It doesn't have to be perfect right now. Just learn the process of working with it all so you can quickly fix it if it sucks.
8. When you get to the code just copy and paste it to notepad so you have it available. Make sure you label each ad cuz they all look alike.
Here's a sample for a 468x15 baner ad.
NOTE 1 - Notice the pub-xxxxxxxxxxxxxxxx - that's your personal publisher number. You'll need that so you might want to always have it available if you use Adsense plugins.
google_ad_client = "pub-xxxxxxxxxxxxxxxxxxx";
google_ad_width = 468;
google_ad_height = 15;
google_ad_format = "468x15_0ads_al_s";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "0000ff";
google_color_text = "000000";
google_color_url = "008000";
9. From there you're ready to paste the adsense code to your site.
10. There's several ways to add adsense to websites and I'm sure Marcus can help you out a lot further on this, but here are 2 ways.
Manual Way - You can use the above code to put the 468x15 banner ad within your blog posts in between paragraphs. Just get your publisher number from your account and replace all those xxxxxx marks with your own Adsense Publisher ID Number. Then go to edit a blog post. Click the "Text" button so you can paste the above code to where you want it. The <div align=center> will center the ad within the article.
Automatic Way - On your blog go to Plugins >> Add Plugins. On the right side you'll see a Search bar. Key in the word "adsense". Choose one of the offered adsense plugins and play with it. If you don't like it, delete it and choose another. Again, you will need your Google Publisher ID number.
11. Test and keep testing
Hope it helps.