Every commit lists one or more parents, possibly several parents, like 8 parents. These commits thus form a graph structure.
Branches and labels are just references to commits in this graph structure; they are commit alias, just a name that references a specific commit. Branches and tags are the same, except by convention the CLI will move branches when you commit to a branch, but tags are not moved by the CLI.
(Commits may have many names, they have their commit ID, and they may also be named by a branch or tag. Commit IDs are hashes of the contents of the commit. This ensures, cryptographically, that a commit and it's ID can never change.)
Git never deletes a commit that is less than 90 days old. If you commit something, rest assured your work is in there somewhere, it's just that no mortal being may be able to find it. Deleting a branch removes a reference to a commit, but the commits in the branch are still there. The GUI tools usually hide commits that are not part of a branch, but you can see them using "reflog" related commands.