A changelist is a set of local changes that have not yet been committed to the VCS repository.
All changes made to your project files are automatically placed in the active changelist (normally, it's the Default changelist, but you can make any other changelist the active changelist).
Create a new changelist
In the Local Changes tab of the Version Control tool window, click and select New Changelist.
In the New Changelist dialog, specify the name of the new changelist, and an optional description.
Set the active changelist
Select a changelist in the Local Changes tab of the Version Control tool window and choose Set Active Changelist from the context menu. All modified files will be automatically placed in this changelist.
Move files between changelists
In the Local Changes tab of the Version Control tool window, select the files that you want to move to another changelist.
Select Move to Another Changelist from the context menu, or under on the toolbar.
In the dialog that opens, select an existing changelist or enter the name for a new changelist.
You can choose to make this changelist the active one, and to track context for it (JetBrains Rider will save the context associated with this changelist, and will restore it when this changelist becomes active).