There are a few ways. Best is to take into account that the size of the screen can be different (mobile, responsive design).
1. create a layout with columns and insert your block into it.
2. add bootstrap grid classes to the block directly ('col-xs-12 col-sm-6 col-md-3' eg to make it resp. full-width, half-width- 1/4-width for extrasmall, small, medium screens)
3. add a custom class to the block: 'myClass' and add custom css:

http://www.anchor-ict.com/blog/concrete5-add-css-block...

Good luck!

Thank you! I will look for option 3, but in regards to option 2, which file is the one that keeps the specific class?

That's saved to the database in CollectionVersionBlockStyles and CollectionVersionBlockStyles (customClass) for the block.
And CollectionVersionThemeCustomStyles for the Theme
The css is saved to StyleCustomizerCustomCssRecords

thank you! The custom class did not work unfortunately at all. In regards to the database, that would be something for sure i want to avoid. i know that for changing header, you edit the header.php and for footer the footer.php. Which one holds the main? I prefer editing the files rather than the database.

Thanks again!

How did it not work ? did you follow the steps in my blog ?
Did you clear the cache ?

Applying changes to the theme files isn't that great to solve this.
What will happen when you upgrade the theme ? And will you still remember these changes in a few years time ?

You can almost always do this with css, but you might have to use a more specific selector.
Anyways, good luck