By default, each new group, block, or symbol is assigned a name automatically. These names are numbered, and the number increases by one whenever you add a new group, block, or symbol to the drawing, ensuring that each has a unique name. By default, the generated names are "Group 1", "Group 2", "Block 1", "Block 2", "Symbol 1," "Symbol 2," and so forth.
You can change the default naming settings in the Auto-Naming page of the Program Setup
The "@" symbol is a placeholder where the actual number will be inserted. For example, if you type "Part @" in the Group name prefix field, the first group you create will automatically be named "Part 1", and the next group will be named "Part 2". If the Group name prefix is "#@ gear," the groups will be named "#1 gear," "#2 gear," etc.

Note: The first ‘@’ that you include in the name is a placeholder for the automatic number. Any ‘@’ characters that occur after the first one will be part of the actual name.

The name of a group or symbol (not a block) is listed on the General page of the Properties window, in the Attribute field. You can use this field to change the name (or path, for a symbol).