I am working on a project, using Fossil for version controlling and organizing it. I have some branches other than my main trunk branch, and want to update (commit) only a single branch. Doing commit will push my changes on a branch to the main Files (i am hosting my project on Chiselapp) . How is it possible to update or commit only a single branch without affecting the main files?
A commit only ever affects a single branch. Except perhaps after merging two branches, but I'm assuming you haven't been doing that.
The only thing I can think of is that the skin you're using has a "Files" menu item that links to dir?ci=tip. The tip is a special name for the most recent commit. Which means that, if you make a commit in a different branch than trunk, that "Files" menu item will now show you the files of that other branch.
The hackish temporary way to fix that is to make a commit in trunk afterwards, so that tip refers to trunk again. But that's not ideal.
The easiest way to permanently fix this, is by choosing a different skin which doesn't do that, or by editing your skin's header, and replacing the link to dir?ci=tip by another link, dir?ci=trunk for example. That way, that menu item will always show the files in the trunk branch.