"Create Record" Action allows to add new record of the selected Object.

• Add an action with the type=Action (1) and Action Type=Create Record (2). See more info about creating Actions in How to create Action article.
• Select the object (3) which you are going to create record for. Add fields you need (4).

• Fill in value for each field. You can use Static values, Merge Fields or Formulas to populate values (see more info on Merge Fields and Formulas at Working with Context objects and  Working with Functions).
• Variable Name (5): you can set a variable which will be populated with the Id of the created record. It's useful if you need to handle successful result of this action and refer to newly created record - e.g., build a link to new record and send it to some user by email.
• Repeat (6): check if you need to create multiple records. When checked, two new fields appear:
• Number of Iterations (7) can contain a number or some variable/merge field returning a number of records to create
• Iterator Name (8): you can set a variable which will be populated with the value of the record creation cycle iterator. It's useful if you need to handle successful result of this action and refer to the index of iterations - e.g., paste it in the record name and send email with it with text like "Record "Case # %iterator_name%" has been created successfully"
• Execute in background (9): select it if you need to execute "Create record" action in other context than current user operation. See more info at How to use Execute in background option. If check this option, the new field will appear:
• With gap (10): by default it is 0, but can be set as an integer number of minutes. This field specifies interval before action execution (for repeated actions - before each iteration).
• Save the action. Now you can call it from SF Process/Flow Builder and other places.