Even If I choose only one branch in git extensions it still shows me something like this. Why are there additional vertical lines? As I found out, red one is branch in my local repo, why is there a separate blue line with tags, why aren't they on red line?

Edit: and what are these circles and rectangles mean? 

![enter image description here](https://i.stack.imgur.com/qUCLM.png)
['https://Stackoverflow.com/questions/20354862', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/260894/']
A git branch is basically a name that points to a commit, but the commit it points to is updated whenever a new commit is added to the branch.

Git is an acyclic directed graph. Each git commit has a) an optional [tree object](http://www.gitguys.com/topics/git-object-tree/), b) an optional parent commit (or two or more parents if it's a merge commit), and c) Commit metadata (committer name, email, commit message, etc.). This means that a branch, which in implementation is just a special auto-updated pointer to a commit, represents the entire subgraph accessible by traversing from that commit along its parents, and their parents, etc. In a history with no merges you will get what you expect; a single straight line of commits. In a history with merges you will see what you have here, multiple paths expanding outward (and merging inwards when a commit started two separate branches which were later merged together.
And for your edit:
The circles represent revisions in the history.
The squares represent a revision which is referenced by one ore more branches.