Karma: “action," “fate,” or “destiny.” Our actions determine our fate. Simple common sense. If I put my hand in a fire (action), I’m going to get burned (fate).
The senses need engagement. Use them to chase after illusory enjoyment, and we're trapped. Use them to serve Krishna, and we're liberated. Easy enough?
A devotee accepts Krishna as the greatest Friend, and any awkward or difficult situation as Krishna’s kindness—meant to bring about some ultimate good.