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?
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, 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.