the blue arrows icons at the bottom of the clip are handles for fine-tune editing of the clips. If you don't see them in your instance of iMovie, iMovie menu > Preferences > Browser > Show Fine Tuning controls are enabled.
the blue gear icon at the bottom of the clip opens up various controls, including the Precision Editor and Clip Trimmer tools.
If you don't see some of the described features in your instance of iMovie, make sure to enable iMovie menu > Preferences > General panel > Show Advanced Tools