how can i place blocks next to each other ?

is it theme dependent or php code dependent

I know that in clean layout for example {geeklog_blocks} creates the blocks but how geeklog understands where to place the second block, and how can i change that ?

anyone ?

blockheader.thtml and blockfooter.thtml are used for placement. Of course header.thtml is used too define the whole page layout. Experiment with those files and see if you can come up with something.

For the most part geeklog is designed to be 2 or 3 columns.