Branch
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A branch adds non-distributed, write isolation to Dolt. A branch can be thought of as a long running transaction. If you have a set of database changes that logically should be grouped together or reviewed together, you make those changes on a branch.
A branch is a named reference that starts with a parent commit. When creating a branch you define it's parent commit and then effectively you have created a new copy of the Dolt database. Changes to the branch only effect that branch. As you commit to the branch the head of the branch changes to the new commit.
You can merge two branches together using the merge command. This creates a commit in the graph with two parents.
Your Dolt database starts with one named branch, main. The name is configurable.
Branches differ from tags which is a named commit that does not change.
Branches can be used on a running Dolt server for write isolation or parallelism. Writes to a branch do not effect another branch until a merge.
In traditional SQL databases, transactions are designed to be short lived. The rows you change in a transaction are essentially locked for the duration of the transaction. Because Dolt allows for merge and more complex conflict resolution than traditional SQL databases, Dolt can essentially support long running transactions on branches.
See for a deeper dive into how to use branches in the SQL server context.
Conceptually Git branches and Dolt branches are the same.
In Dolt, branches become a slightly more important concept in server mode. In Git, you often are working on a clone of your repository locally. Thus, your write isolation can be at the clone level. With Dolt in server mode, your application will be coordinating writes to a single server through branches.