How do I learn to operate a vessel on my own?

Following orders is one thing. Being the one who gives them, who holds the whole vessel in your hands, is another entirely. That it overwhelms you makes sense. You are looking at the full weight of it at once instead of the pieces you would actually carry one at a time. No captain started as a captain. Every one of them was once a hand who did as they were told, then slowly took on more: a watch, a maneuver, a decision, a passage. Ask to be given the helm in safe conditions with an experienced operator beside you. Do the small responsibilities first. Competence grows by degrees, not in a single leap. Pick one skill to own this month. Reading the chart, docking, holding a heading, whatever feels most within reach. Master that, then add the next. The overwhelm comes from seeing the mountain whole. You climb it the only way anyone does: one steady step at a time, until one day you realize the vessel answers to you.