How do I start my e-commerce business with digital marketing?

Research Ecommerce Business Models using Google or other sources. Start Ecommerce Niche Research, try use this to figure out what markets you can fit into. Validate your Target Market and think up some product ideas to fill that market. Register Your Ecommerce Business and brand name. Finalize Your Ecommerce Business Plan and Create Your Online Store.

Finally, make your online store, create the UI and off you go.