Problems in understanding

html and css

I already have visited a elementary html course, but never finished. So, I started just by trying out. I worked and I still work with brackets. It was easy for example to implemet a backbround image, to write a text and change the appereance of the headline or other text styles, but I had problems to implement a sidebar. After I tried to use some existing codes from http://www.w3schools.com it looked:

and then:

and:

When I was not able to solve the problem by my own, I asked Daniele to help me and he tidied up my code and helped me to build a table instead of a sidebar.
I think the code of the sidebar did not run, because of several mistakes. I forgot to close some orders, for examples. That is the first and one of the most important things you have to be aware of. Remember: close each order you opend before!
In the meanwhile I recognize that tables are not the very best way building web pages and I tried a lot to change my web page into a respensive page, but I have still problems. Now have a look on my code:

With the order table you open it. Inseide the brackets you define the rows and colums of your table.
The order for rows is tr, td is the order for a column. The right way to use the oders is: open > table open > tr first row open > td text/image close > td open td text/image close > td close > tr open > tr second row and so on ...
I also created a class and named it table_class. td > creats the first space of the first column

git repository

As you can read above, I have had also problems in understanding git and in the beginning I installed a false version. It was: git-2.10.1-intel-universal-mavericks. My system is too old for it. After recognizing the problem I installed git-2.2.1-intel-universal-snow-leopard. This version runs on my mac version 10.8.5. Now I have had just to try it out: