Debug - Step Into

At design time:

Ribbon bar. Select the Debug tab. In the Step group, click Into to begin running the macro in break mode.

Classic menus. From the Debug menu, select Step Into to begin running the macro in break mode.

Selecting Step Into again will execute the currently paused line of code and move the focus to the next line (without executing it). If an external function is called, then the steps within that function will be stepped through in the same manner.

Note that this command can also be executed by pressing F8. See also Debug - Step Out, Debug - Step Over, and Debug - Run to Cursor.